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    <title>Darshan Chheda</title>
    <description>Graduate Software Engineer in London building AI pipelines, full-stack apps, and cloud-native systems with TypeScript, React, Node.js, Python, and DevOps.</description>
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    <pubDate>Wed, 20 May 2026 00:00:00 GMT</pubDate>
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      <title>Cortex: Your AI Agent Is Reading Your Code Wrong</title>
      <link>https://www.darshanchheda.com/posts/cortex</link>
      <guid isPermaLink="true">https://www.darshanchheda.com/posts/cortex</guid>
      <pubDate>Wed, 20 May 2026 00:00:00 GMT</pubDate>
      <updated>2026-05-20T00:00:00.000Z</updated>
      <dc:creator>Darshan Chheda</dc:creator>
      <description><![CDATA[AI agents waste 99% of their context scanning raw source code. Cortex is a zero-dependency Rust engine that pre-computes local call graphs, traces taint paths, and persists agent memory over MCP.]]></description>
      <content:encoded><![CDATA[<img src="https://www.darshanchheda.com/_astro/image.tBMk9_O4.jpg" alt="Cortex: Your AI Agent Is Reading Your Code Wrong" style="width: 100%; height: auto; margin-bottom: 1em;" />
<h2>The problem with how agents read code</h2>
<p>Every AI coding agent in 2026 does the same thing when you ask a structural question: it reads your files. Every single time.</p>
<p>Ask Claude Code, Cursor, or Cline something like “What calls <code>processOrder</code>?” and watch the terminal. The agent opens a file, scans it line by line, finds an import, opens another file, and keeps going. It can easily burn 20,000 tokens on raw source code just to trace a single caller relationship. Start a new session five minutes later and ask the same question, and it does the whole thing again from scratch. It retained nothing.</p>
<p>This is not a model intelligence problem. Frontier models like GPT-5, Claude Sonnet 4.5, or Gemini 3.1 Pro reason incredibly well. The issue is the interface layer between the agent and your codebase. The agent receives unstructured text when it needs structure. It gets raw files when it needs call relationships. A massive stream of data, when what it actually wanted was a single connection.</p>
<hr />
<h2>Why bigger context windows are not the answer</h2>
<p>The obvious fix is a larger context window. A million tokens sounds like plenty. But research keeps showing that throwing more context at agents does not make them better, it often makes them worse.</p>
<p>A Chroma Research study, “Context Rot: How Increasing Input Tokens Impacts LLM Performance” (July 2025) tested 18 frontier models across repository-scale tasks. Every model showed measurable performance degradation as input length grew — not a sudden cliff at the end of the context window, but a steady, continuous decline in reasoning quality. A separate 2025 study on long-context models found this degradation happens even when retrieval is perfect. The problem is not whether the right information is in the context. It is how much irrelevant noise surrounds it.</p>
<p>When you flood an agent’s context with raw file content, it has to spend its attention parsing boilerplate code, comments, and imports just to find the one relationship it needed. The more files it reads, the more its accuracy on the next step drops.</p>
<p>The academic research on this has been converging on a common answer. GraphCoder (Liu et al., 2024) proposed retrieving code contexts via a structural graph rather than text similarity, yielding a +6.06 improvement in exact-match code completion while using less time and memory. CodexGraph (Liu et al., 2024) built on that by replacing file-reading with structured graph queries against a codebase-wide code graph. Both studies reached the same conclusion: for repository-scale tasks, structure beats raw text.</p>
<hr />
<h2>The Jail House Lock problem</h2>
<p>If you have read or watched JoJo’s Bizarre Adventure Stone Ocean, you know exactly what this failure mode feels like.</p>
<p>There is a Stand named Jail House Lock, used by Miu Miu. Its ability is simple but terrifying: it limits its victim to holding only three new pieces of information in their working memory at a time. Learn a fourth thing and the first one disappears. The victim is not made less intelligent. Their reasoning remains intact. They just cannot hold enough context to act on what they know.</p>
<figure><img src="https://www.darshanchheda.com/_astro/jojo.BXkBIkHT.gif" alt="Jail House Lock Stand ability" /><figcaption>Jolyne’s memory fragmenting under Jail House Lock.</figcaption></figure>
<p>This is exactly what happens to AI coding agents today.</p>
<p>A medium-sized codebase is typically on the order of hundreds of thousands to a few million tokens (roughly 500k–2M), depending on language and code density. An agent cannot fit all of that into context, so it reads files one at a time, forgets what it read three files ago, and makes architectural decisions based on whatever fragment happens to be in its memory right now.</p>
<p>Miu Miu’s strategy in the story is to flood Jolyne with distractions, like counting individual bullets or reading prison signs, so the crucial details get pushed out. Every file an agent reads that is not directly relevant to the task works the same way, pushing out the structural map of your codebase.</p>
<p>Jolyne’s solution is elegant. She stops trying to memorize individual facts and instead learns to look at a reflected image in a mirror to see all the bullets at once, compressing many facts into a single unit.</p>
<p>That is the core idea behind Cortex. It pre-computes the structural relationships in your codebase and serves them as a single, compressed unit. The agent gets a complete answer about callers, callees, or blast radius in one response costing a few hundred tokens. Its context window stays free for actual reasoning.</p>
<hr />
<h2>How agents work today vs. how they should work</h2>
<figure><img src="https://www.darshanchheda.com/_astro/comparison.DJoHpAeG.png" alt="Standard AI agent context consumption vs. Cortex graph-based traversal" /><figcaption>How standard AI agents consume codebases (by scanning files textually) versus the Cortex graph-based traversal approach</figcaption></figure>
<p>The difference is not incremental. If you ask an agent what breaks if you change a core database pool function, the standard approach forces the agent to trace imports recursively across dozens of files. That can easily cost tens of thousands of tokens (e.g., 20k–100k). Cortex answers that same query with a breadth-first traversal in less than 1,000 tokens. That represents a 100x reduction on a single query.</p>
<p>Over a typical coding session where an agent makes 20 to 40 structural queries, the savings compound. The agent stays within its context budget and can actually reason about the answers instead of forgetting them.</p>
<hr />
<h2>What is actually in the landscape right now</h2>
<p>Before looking at how Cortex works, it is worth exploring what else exists in the developer tool space and where each approach makes compromises.</p>
<ul>
<li><strong>Repomix:</strong> The most popular tool by stars, Repomix packs your entire repository into a single, clean text file with token counting and security checks. The constraint is that it is a one-shot dump. The agent still reads everything. There is no session memory, no delta awareness, and no structural query interface. It works well for small projects, but it quickly fills up the context window on larger codebases.</li>
<li><strong>LeanCTX:</strong> A highly feature-complete tool. It includes delta reads, shell output compression, session checkpoints, and a dashboard showing token savings. Its main challenge is complexity: it exposes ~58 different tools (as of Q1 2026), which creates a large system prompt overhead for the agent.</li>
<li><strong>codebase-memory-mcp:</strong> Built in Zig, this tool performs call graph tracing, cross-service HTTP linking, and dead code detection. It has a fast setup but lacks cross-session memory and shell output compression.</li>
<li><strong>Engram:</strong> Operating entirely locally without GPUs or cloud APIs, Engram intercepts file reads and returns structural summaries instead of full file content. It is extremely efficient but is limited to a few core languages.</li>
<li><strong>Serena:</strong> This tool uses the Language Server Protocol (LSP) to provide highly precise type information. It excels at type-level queries but requires setting up and running active language servers for each language in your project, making it more complex to deploy.</li>
</ul>
<p>None of these tools combine graph-based structural intelligence, cross-session memory with automatic staleness invalidation, built-in security analysis, and a zero-dependency binary that configures itself for multiple agents.</p>
<hr />
<h2>What Cortex actually is</h2>
<p>Cortex is a single Rust binary. It does not require a Python runtime, Docker, cloud API keys, or active language servers. When you run <code>cortex index</code>, it uses tree-sitter to parse your repository, extracting functions, classes, call edges, import relationships, and data flows, storing them in a local SQLite database. When you run <code>cortex serve</code>, it exposes this structural graph over the Model Context Protocol (MCP) using a standard JSON-RPC 2.0 stdio interface.</p>
<p>Any MCP-compatible agent can connect to it immediately. This includes Claude Code, Cursor, Copilot, Cline, Zed, JetBrains, and many others. The agent can use 32 granular tools, or run in smart mode where a single <code>ask</code> meta-tool routes requests internally.</p>
<p>The graph stays updated automatically. A background file watcher listens for native OS file events and triggers incremental re-indexing whenever you save a file. Re-indexing a changed file takes less than 15 milliseconds, ensuring the agent always queries current code.</p>
<pre><code># Set up Cortex in under 30 seconds
npx @1337xcode/cortex install   # downloads binary, detects agents, writes config
cortex index                     # builds the call graph (127 files in 535ms)
</code></pre>
<p>The installer detects your active IDEs and agents, writing the correct configuration entries automatically without requiring manual JSON editing.</p>
<hr />
<h2>Who uses this and why</h2>
<p>Cortex is designed for a few distinct development workflows:</p>
<ul>
<li><strong>Vibe Coders:</strong> Developers who rely heavily on AI agents to write code. For these users, Cortex prevents the agent from getting lost in large codebases. The agent has a structural map, so it makes fewer mistakes and stays oriented during long coding sessions.</li>
<li><strong>Senior Architects:</strong> Teams that need to map out legacy systems. Cortex can generate architectural overviews, find dead code, and run community detection to visualize how modules are coupled in reality versus their intended design.</li>
<li><strong>Migration Engineers:</strong> Developers tasking agents with refactoring legacy code. Cortex helps the agent calculate the blast radius of changing a function, showing exactly how many upstream files will be affected before a line of code is modified.</li>
<li><strong>Security &amp; Platform Teams:</strong> Teams that want basic security scans without setting up heavy SAST pipelines. Cortex can scan for OWASP patterns, trace user input to sensitive sinks, and generate SPDX SBOMs locally.</li>
</ul>
<hr />
<h2>Architecture: three subsystems in one process</h2>
<p>Cortex runs three concurrent subsystems inside a single process:</p>
<figure><img src="https://www.darshanchheda.com/_astro/architecture.DTWiZSze.png" alt="Cortex architecture" /><figcaption>Cortex architecture: File Watcher, Indexer, and MCP subsystems running concurrently inside a single process, backed by SQLite WAL mode</figcaption></figure>
<ul>
<li><strong>The Indexer:</strong> Walks the filesystem, parses source files in parallel using Rayon, extracts symbols and edges, and writes them to SQLite. It uses a two-pass resolution strategy for cross-file call edges: the first pass collects definitions to build a symbol table, and the second pass resolves call targets against it.</li>
<li><strong>The File Watcher:</strong> Uses the <code>notify</code> crate to listen to native OS events like <code>inotify</code>, <code>FSEvents</code>, or <code>ReadDirectoryChangesW</code>. When you save a file, it tells the indexer to re-process only that file. If the SHA-256 hash of the file is unchanged, the update completes in about 13 milliseconds.</li>
<li><strong>The MCP Server:</strong> Runs on a Tokio async runtime to handle concurrent tool requests. It communicates over stdio using JSON-RPC 2.0. SQLite’s Write-Ahead Logging (WAL) mode enables readers to query the database concurrently without blocking the indexer writes.</li>
</ul>
<figure><img src="https://www.darshanchheda.com/_astro/pipeline.Bb2P3wEs.png" alt="Sequence diagram of the file change and query resolution pipeline" /><figcaption>Sequence diagram showing the asynchronous file watcher triggering single-file re-indexing in SQLite WAL mode while the MCP server concurrently serves the agent</figcaption></figure>
<hr />
<h2>The Indexer Pipeline</h2>
<figure><img src="https://www.darshanchheda.com/_astro/indexer.D3golkxD.png" alt="Cortex indexer pipeline" /><figcaption>The Cortex indexer pipeline: from file change detection and AST parsing to FQN resolution and observation invalidation</figcaption></figure>
<p>The indexer supports 29 languages. 26 use compiled tree-sitter grammars that are statically linked into the binary (no runtime downloads, no external grammar files). Three languages (Kotlin, SQL, Perl) use regex-based extraction as a fallback because their tree-sitter grammar crates have version conflicts with the rest of the tree-sitter ecosystem.</p>
<p>Languages are tiered by extraction quality based on how much structural information the grammar queries can extract:</p>
<ul>
<li><strong>Tier 1 (Full call graph, imports, routes):</strong> Python, TypeScript, JavaScript, Rust, Go, and Java. These are the languages where Cortex’s structural analysis is most complete. If your codebase is primarily in one of these languages, you get the full benefit of blast radius analysis, taint flow tracing, and cross-file call resolution.</li>
<li><strong>Tier 2 (Symbols + partial call edges):</strong> C#, C++, Ruby, Swift, Scala, PHP, and Dart. The graph is useful but may miss some indirect calls or complex dispatch patterns.</li>
<li><strong>Tier 3 (Symbol extraction, limited edges):</strong> The remaining languages (Haskell, Elixir, Lua, Zig, Bash, R, Objective-C, OCaml, Julia, HCL/Terraform, YAML). You still get function and class definitions indexed, searchable, and visible in the architecture overview. However, call graph edges are sparse.</li>
</ul>
<p>Parsing is parallelized with Rayon. Each file gets its own tree-sitter parser instance on a thread pool worker. The work-stealing scheduler means fast files do not block slow files. For a 3,500-file Python project (the CPython standard library), full indexing completes in under 60 seconds. A typical 100-file web application takes about 500ms. Large repositories (50K+ files) are processed in batches of 500 to avoid memory exhaustion.</p>
<p>The tree-sitter grammars are compiled from source at build time via the <code>cc</code> crate (each grammar crate includes its own <code>build.rs</code>). No network downloads occur during compilation. All 26 grammar C sources are vendored within their respective crates.</p>
<hr />
<h2>The database schema</h2>
<p>Cortex uses SQLite in WAL (Write-Ahead Logging) mode. WAL allows concurrent readers while a single writer operates, which maps perfectly to the architecture: many MCP tool calls reading simultaneously, one indexer writing.</p>
<figure><img src="https://www.darshanchheda.com/_astro/database.DQcHSbjH.png" alt="Cortex database schema" /><figcaption>SQLite database schema: tables representing nodes, edges, file snapshots, observations, taint paths, and security findings</figcaption></figure>
<p>On top of the core tables, Cortex maintains:</p>
<ul>
<li><strong>FTS5 virtual table</strong> (<code>nodes_fts</code>) for full-text search over FQN, kind, file, and attributes. Uses the <code>unicode61</code> tokenizer with BM25 ranking (k1=1.2, b=0.75). Kept in sync via INSERT/UPDATE/DELETE triggers.</li>
<li><strong>Vector embeddings table</strong> (<code>node_embeddings</code>) for optional semantic search via sqlite-vec and a local ONNX model (nomic-embed-text-v1.5, 768-dimensional embeddings).</li>
<li><strong>SBOM entries</strong> for dependency tracking extracted from lock files.</li>
</ul>
<hr />
<h2>Smart tool routing &amp; the 32 MCP tools</h2>
<p>Exposing 32 different tools to an agent creates a lot of context overhead. Each tool definition, along with its schema, description, and arguments, consumes tokens just to be present in the system prompt. Exposing all 32 tools costs approximately 4,000 to 6,000 tokens of the agent’s context window before the session even starts.</p>
<p>Smart mode (<code>cortex serve --smart-tools</code>) reduces this to just 5 tools. The <code>ask</code> meta-tool accepts a natural language question, extracts the user’s intent and symbol references, routes it internally to the appropriate graph queries, and returns a unified answer. The agent interacts with one tool instead of 32, dropping context overhead by 89%.</p>
<pre><code>// Simplified routing logic from src/mcp/ask.rs
fn route_question(question: &amp;str) -&gt; Vec&lt;InternalTool&gt; {
    if contains_pattern(question, &amp;["what calls", "who calls"]) {
        vec![InternalTool::TraceCallers]
    } else if contains_pattern(question, &amp;["what does", "call"]) {
        vec![InternalTool::TraceCallees]
    } else if contains_pattern(question, &amp;["breaks", "impact", "change"]) {
        vec![InternalTool::BlastRadius]
    } else if contains_pattern(question, &amp;["security", "taint", "vuln"]) {
        vec![InternalTool::FindTaintPaths, InternalTool::ScanOwasp]
    } else if contains_pattern(question, &amp;["dead code", "unused"]) {
        vec![InternalTool::FindDeadCode]
    } else if contains_pattern(question, &amp;["architecture", "overview"]) {
        vec![InternalTool::GetArchitecture]
    } else {
        // Fallback: search symbols + full text
        vec![InternalTool::SearchSymbols, InternalTool::SearchText]
    }
}
</code></pre>
<p>The tool categories cover:</p>








































<table><thead><tr><th>Category</th><th>Tools</th><th>What they answer</th></tr></thead><tbody><tr><td>Structural</td><td><code>search_symbols</code>, <code>trace_callers</code>, <code>trace_callees</code>, <code>get_file_context</code>, <code>get_architecture</code>, <code>find_dead_code</code>, <code>blast_radius</code>, <code>detect_changes</code>, <code>get_code_snippet</code>, <code>query_graph</code></td><td>”What is this? Who uses it? What depends on it?”</td></tr><tr><td>Search</td><td><code>search_text</code>, <code>semantic_search</code></td><td>”Find me something by name or concept”</td></tr><tr><td>HTTP</td><td><code>get_http_routes</code>, <code>trace_http_call</code></td><td>”What endpoints exist? Where does this call go?”</td></tr><tr><td>Security</td><td><code>find_taint_paths</code>, <code>scan_owasp</code>, <code>generate_sbom</code>, <code>check_dependencies</code></td><td>”Is this code vulnerable? What are we importing?”</td></tr><tr><td>Memory</td><td><code>write_observation</code>, <code>read_observations</code>, <code>write_adr</code>, <code>read_adrs</code>, <code>prune_observations</code></td><td>”Remember this. What did we learn before?”</td></tr><tr><td>Analysis</td><td><code>decompose_boundaries</code>, <code>get_complexity_hotspots</code>, <code>get_task_context</code>, <code>generate_steering</code>, <code>get_class_hierarchy</code>, <code>get_git_hotspots</code>, <code>get_import_graph</code>, <code>find_similar_functions</code></td><td>”How is this codebase organized? Where are the risks?”</td></tr></tbody></table>
<hr />
<h2>Cross-session memory and why staleness matters</h2>
<p>This is the feature that separates Cortex from a static index. Every other tool in this space treats each session as independent. The agent starts fresh every time, forgetting what it learned about your codebase yesterday.</p>
<p>Cortex maintains a persistent memory layer. When an agent learns something about your code, it can write that observation to Cortex, linked to the specific code symbol’s fully qualified name. The observation persists in SQLite across sessions, agent restarts, and machine reboots.</p>
<p>The engineering challenge here is trust. If an agent wrote “this function uses HMAC-SHA256 for token validation” three weeks ago, and a developer has since changed the function to use Ed25519, that old observation is now wrong. An agent that blindly trusts old observations will make incorrect decisions.</p>
<p>Cortex solves this with staleness invalidation. Every observation records the <code>node_hash_at_write</code>, which is the SHA-256 hash of the linked code at the time the observation was written. When the indexer re-processes a file and detects that a node’s content hash has changed, it marks all linked observations as <code>stale</code>. The observation still surfaces in query results, but with <code>is_stale: true</code> so the agent knows to verify it before relying on it.</p>
<figure><img src="https://www.darshanchheda.com/_astro/session.DfXkQAAg.png" alt="Cross-session memory lifecycle" /><figcaption>Cross-session memory lifecycle: writing observations, detecting code changes, marking observations as stale, and subsequent agent reading</figcaption></figure>
<p>This creates a feedback loop. Agents build institutional knowledge about the codebase over time, and that knowledge degrades gracefully when the code changes. Stale observations are not deleted because they might still be partially correct or historically useful. They are simply flagged so the agent can make an informed decision.</p>
<p>Architectural Decision Records (ADRs) work the same way. An agent can record “we chose connection pooling over per-request connections because the connection setup latency was dominating request time” linked to the database module. Future agents can read these decisions and understand the reasoning behind the current architecture without asking the developer to explain it again.</p>
<p>For teams where multiple agents work on the same codebase, the memory layer becomes shared institutional knowledge. Agent A’s observations about the API contract are visible to Agent B when it is working on the frontend that consumes that API.</p>
<hr />
<h2>Security analysis on the structural graph</h2>
<p>Most security scanning tools operate on one of two levels. Static analysis tools (Semgrep, CodeQL) pattern-match against source text or AST patterns within single files. Dynamic analysis tools probe running applications. Both require significant setup and often cloud infrastructure.</p>
<p>Cortex takes a different approach. It runs security analysis on the structural call graph that already exists from indexing. There is no additional scanning pass, no cloud APIs, and no paid subscriptions.</p>
<ul>
<li><strong>Taint flow analysis:</strong> Traces data from user-input sources through the call graph to sensitive sinks. Sources include HTTP request parameters (Flask <code>request.args</code>, FastAPI path parameters, Express <code>req.body</code>, Go <code>r.FormValue</code>), environment variables, and file reads. Sinks include raw SQL queries, file writes with user-controlled paths, and shell command execution (<code>os.system</code>, <code>subprocess.run</code>, <code>exec</code>). The analysis follows call edges up to depth 5 for inter-procedural propagation. If function A reads user input and passes it to function B which passes it to function C which executes a SQL query, Cortex traces that full path.</li>
<li><strong>OWASP Top 10 pattern detection:</strong> Runs against the structural graph, not just regex over source text. It detects patterns for A01 (Broken Access Control, functions that access resources without checking permissions), A02 (Cryptographic Failures, use of weak algorithms or hardcoded keys), A03 (Injection, unsanitized input reaching query construction), and A04 (Insecure Design, missing validation on trust boundaries). Each finding includes a confidence score and CWE classification.</li>
<li><strong>SBOM generation:</strong> Generates software bills of materials in SPDX 2.3 format by extracting dependencies from the import graph and cross-referencing them with lock files. It reads Cargo.lock, package-lock.json, go.sum, requirements.txt, pyproject.toml, and Gemfile to get exact versions. The <code>check_dependencies</code> tool then queries OSV.dev for known CVEs against those versions.</li>
</ul>
<pre><code># Full security workflow
cortex security scan          # taint flows + OWASP patterns
cortex security sbom          # SPDX 2.3 dependency list
cortex security vulns         # cross-reference against OSV.dev (requires network)
cortex security report        # human-readable summary of all findings

# CI integration with quality gates
cortex ci --fail-on-taint --fail-on-owasp    # exit code 1 if issues found
cortex ci --fail-on-dead-code-above 15       # exit 1 if dead code exceeds 15%
cortex ci --format json                       # machine-readable output for CI dashboards
</code></pre>
<p>The taint analysis is structural, not symbolic execution. It will not catch every vulnerability that a dedicated SAST tool like CodeQL would find. It does not reason about string concatenation patterns or complex control flow within a single function. But it catches the common inter-procedural patterns (unsanitized HTTP input reaching SQL queries across function boundaries, user data flowing through three function calls to reach command execution) with zero configuration and zero cloud dependencies. No other tool in this space offers any security analysis at all.</p>
<hr />
<h2>Hybrid search and why three layers matter</h2>
<p>Search in Cortex is not a single mechanism. It is three layers that activate in sequence based on result quality.</p>
<ul>
<li><strong>Layer 1: The graph index.</strong> When an agent calls <code>search_symbols</code> with a pattern like <code>*UserService*</code>, Cortex first tries exact and glob pattern matching against fully qualified names in the nodes table. This is fast and precise. If it returns 3 or more results, the search stops here.</li>
<li><strong>Layer 2: FTS5 BM25.</strong> If the graph index returns fewer than 3 results, Cortex automatically falls back to full-text search over the FTS5 virtual table. This catches cases where the agent’s search term does not match the FQN pattern but does appear in the symbol name, file path, or attributes. BM25 ranking produces relevance-sorted results.</li>
<li><strong>Layer 3: Vector similarity (optional).</strong> When enabled via <code>cortex semantic enable</code>, the <code>semantic_search</code> tool performs cosine similarity search over 768-dimensional embeddings generated by a local ONNX model (nomic-embed-text-v1.5). This handles conceptual queries like “find functions that handle authentication” where the word “authentication” might not appear in any symbol name.</li>
</ul>
<p>Results from layers 1 and 2 are merged and deduplicated by FQN, sorted by confidence descending. The response includes <code>_meta.retrieval_method</code> (“graph”, “fts5”, or “hybrid”) so the agent knows how the results were found and can adjust its confidence accordingly.</p>
<p>The model for semantic search runs locally with no network calls after the initial 138 MB download, meaning it works in air-gapped environments. The embeddings are stored in SQLite via sqlite-vec, which is compiled as a loadable extension and statically linked into the binary. No external vector database is needed.</p>
<hr />
<h2>Multi-repo federation and cross-service intelligence</h2>
<p>Real projects are rarely a single repository. You have a frontend, a backend API, a shared library, maybe an auth service and a notification service. Each lives in its own repo. An agent working in the frontend repo has no visibility into the backend’s structure unless you give it that visibility.</p>
<pre><code>cortex federate add ../auth-service
cortex federate add ../shared-lib
cortex federate add ../notification-service
cortex federate list
</code></pre>
<p>Each federated repository must have its own <code>.cortex/</code> directory (run <code>cortex index</code> there first). Once federated, all MCP queries search across all member repos transparently. “What calls <code>AuthService.validateToken</code>?” returns results from every repository in the federation.</p>
<p>The cross-service HTTP linking is where this gets interesting for microservice architectures. If the frontend makes a <code>fetch("/api/users")</code> call and the backend has a route handler registered for <code>GET /api/users</code>, Cortex creates an <code>HttpLink</code> edge between them with a confidence score. The agent can trace a request from the frontend button click through the API gateway to the backend handler to the database query, across repository boundaries, in one tool call.</p>
<p>For system engineers managing microservice architectures, this answers questions that normally require grepping through 15 repositories. “Which services are affected if I change the <code>/api/auth/refresh</code> endpoint?” becomes a single <code>blast_radius</code> query across the federation.</p>
<hr />
<h2>Build system awareness and module boundary detection</h2>
<p>Cortex understands workspace structures for five build systems:</p>
<ul>
<li><strong>Cargo workspaces</strong> (Rust) by reading <code>Cargo.toml</code> <code>[workspace]</code> members</li>
<li><strong>npm workspaces</strong> (Node.js) by reading <code>package.json</code> <code>workspaces</code> field</li>
<li><strong>Go workspaces</strong> by reading <code>go.work</code> file</li>
<li><strong>Gradle multi-module</strong> by reading <code>settings.gradle</code></li>
<li><strong>Maven multi-module</strong> by reading parent <code>pom.xml</code></li>
</ul>
<p><code>cortex modules --build-system</code> shows workspace members as defined by the build configuration. This is the intended module structure.</p>
<p><code>cortex modules</code> (without the flag) runs Leiden community detection on the call graph and shows clusters of tightly-coupled code based on actual call relationships. This is the actual module structure.</p>
<p>Comparing the two reveals architectural drift: code that the build system says belongs in module A but the call graph shows is actually tightly coupled to module B. This is the kind of insight that normally requires a senior architect spending a week with a whiteboard. Cortex produces it from graph analysis in under a second.</p>
<hr />
<h2>Git intelligence and risk scoring</h2>
<p>Code that changes frequently and has many callers is the highest-risk code in any repository. A bug in that code affects the most downstream consumers, and a breaking change in that code requires the most coordination.</p>
<p>Cortex combines git commit history with the call graph to surface these hotspots:</p>
<pre><code>cortex hotspots --months 6 --limit 20
</code></pre>
<p>Risk score formula: <code>churn_count * caller_count</code>. A function that changed 15 times in 6 months and has 30 callers scores 450. A function that changed once and has 2 callers scores 2. The high-scoring functions are where bugs are most likely to appear and where changes have the widest blast radius. This is a direct measurement of volatility multiplied by impact.</p>
<p>Coverage gap analysis cross-references LCOV test coverage data with the call graph:</p>
<pre><code>cortex coverage --lcov coverage.lcov
</code></pre>
<p>This produces a ranked list of untested functions sorted by how many other functions call them. An untested utility function with 50 callers is a higher-priority coverage gap than an untested leaf function with 0 callers. Standard coverage tools tell you what percentage of lines are covered. Cortex tells you which uncovered functions are the most dangerous to leave untested.</p>
<p>It supports LCOV files generated by cargo-tarpaulin, jest, pytest-cov, gcov, llvm-cov, istanbul, and any tool that produces standard LCOV format.</p>
<hr />
<h2>3D visualization</h2>
<pre><code>cortex viz --export graph.html
</code></pre>
<p>This generates a standalone HTML file with an embedded 3D force-directed graph using <code>3d-force-graph</code>. Nodes are colored by Leiden community assignment and sized by caller count. You can rotate, zoom, click nodes to see their details, and visually identify clusters and bottlenecks.</p>
<p>The visualization is self-contained. No server is needed after export; you can open the HTML file in any browser. It is useful for onboarding new team members, architecture review meetings, and identifying god classes (oversized nodes with dozens of edges).</p>
<p>For the interactive version during development, <code>cortex viz --port 9749</code> starts a local HTTP server with live updates as the graph changes.</p>
<hr />
<h2>The bundle format and team sharing</h2>
<p><code>cortex bundle export</code> serializes the full graph (nodes, edges, observations, ADRs, security findings) to a JSON file called <code>cortex.json</code>. This file can be committed to git.</p>
<p>Why JSON and not the SQLite database file? Three reasons:</p>
<ol>
<li><strong>JSON is diffable in pull requests.</strong> You can see what structural relationships changed between commits. “This PR added 3 new call edges to the auth module” is visible in the diff.</li>
<li><strong>Adding fields is backward-compatible.</strong> New versions of Cortex can add fields to the bundle without breaking old bundles. Old versions ignore unknown fields.</li>
<li><strong>Developers can read it.</strong> Open <code>cortex.json</code> in any text editor and see the observations your team’s agents wrote, the architectural decisions recorded, and the security findings flagged. No SQLite client is needed.</li>
</ol>
<pre><code># Developer A indexes and exports
cortex index &amp;&amp; cortex bundle export
git add cortex.json &amp;&amp; git commit -m "update graph bundle"

# Developer B pulls and imports (skips indexing entirely)
git pull &amp;&amp; cortex bundle import
cortex serve   # ready to query immediately
</code></pre>
<p>For teams where not everyone wants to install Cortex locally, the bundle means the graph is available as a readable JSON artifact in the repository. CI can generate it on every push. The bundle also supports CCG (Code Context Graph) export format via <code>--format ccg</code> for interoperability with other tools.</p>
<hr />
<h2>Design decisions and the reasoning behind them</h2>
<h3>Why Rust</h3>
<p>Not for the meme, but for three concrete engineering reasons:</p>
<ul>
<li><strong>Single binary distribution:</strong> <code>cargo build --release</code> produces one executable with no runtime dependencies. No Python interpreter version conflicts, no Node.js, no JVM, and no Docker. The user downloads a binary and it works on their machine regardless of what else is installed. This matters because Cortex needs to run on developer machines with unpredictable environments, in CI containers, and on air-gapped workstations.</li>
<li><strong>Tree-sitter FFI:</strong> Tree-sitter is a C library, and Rust’s FFI with C is zero-cost at runtime. The tree-sitter grammar crates compile their C sources via the <code>cc</code> crate at build time and link statically. No dynamic library loading, no PATH issues, and no version conflicts between grammars.</li>
<li><strong>Rayon for parallelism:</strong> Parsing 3,500 files needs to be fast. Rayon’s work-stealing thread pool makes parallel file parsing trivial. The code is essentially <code>files.par_iter().map(|f| parse(f)).collect()</code>. There is no manual thread management, no async complexity for CPU-bound work, and no race conditions on the parser instances because each thread gets its own.</li>
</ul>
<h3>Why SQLite over a graph database</h3>
<p>The obvious choice for a call graph would be Neo4j or DGraph or some purpose-built graph database. Cortex uses SQLite instead:</p>
<ul>
<li><strong>Zero configuration:</strong> No server process to start, no connection strings to configure, no Docker compose files, and no port allocation. The database is a single file at <code>.cortex/graph.db</code>.</li>
<li><strong>WAL mode gives the exact concurrency pattern needed:</strong> Multiple concurrent readers (MCP tool calls) alongside a single writer (the indexer). No reader ever blocks, and the writer does not block readers.</li>
<li><strong>FTS5 is built in:</strong> Full-text search with BM25 ranking without deploying Elasticsearch or Meilisearch. One less dependency, one less process, and one less thing that can break.</li>
<li><strong>sqlite-vec for vectors:</strong> Optional semantic search without Pinecone or Qdrant. The vector index lives in the same database file.</li>
<li><strong>Portability:</strong> The database file works on every OS without conversion.</li>
</ul>
<p>The tradeoff is that SQLite’s single-writer constraint means indexing writes are serial. In practice, this does not matter because the bottleneck is parsing (parallelized with Rayon), not writing. The write phase for a typical index run is under 50ms, while the parse phase is 500ms to 60 seconds depending on codebase size.</p>
<h3>Why MCP over stdio instead of HTTP</h3>
<p>The Model Context Protocol uses JSON-RPC 2.0 over stdio (stdin/stdout). This is the simplest possible transport:</p>
<ul>
<li>No port allocation conflicts (multiple Cortex instances can run simultaneously for different projects).</li>
<li>No TLS certificate management.</li>
<li>No firewall rules or CORS configuration.</li>
<li>The agent process spawns Cortex as a child process and communicates via pipes.</li>
</ul>
<p>Every MCP-compatible agent already knows how to do this. Cortex reads JSON from stdin, writes JSON to stdout, and logs to stderr. The protocol is stateless at the transport level, and state lives in the SQLite database, not in the connection.</p>
<h3>Why not LSP</h3>
<p>The Language Server Protocol (LSP) is designed for IDE features like autocomplete, go-to-definition, and hover information. It is optimized for single-file, cursor-position queries: “What is the type of the variable at line 42, column 15?”</p>
<p>Cortex answers cross-codebase structural questions: “What is the blast radius of changing this function?” “What are the module boundaries?” “Where does user input flow to SQL queries?” LSP has no concept of blast radius, community detection, taint flow analysis, or cross-session memory.</p>
<p>LSP also requires per-language server implementations (rust-analyzer for Rust, pyright for Python, tsserver for TypeScript, gopls for Go). Each is a separate process with its own memory footprint and startup time. Cortex handles 29 languages with one binary because tree-sitter grammars are language-agnostic at the API level.</p>
<p>The tradeoff is precision. LSP-based tools like Serena have exact type information. They know that <code>foo</code> is a <code>Vec&lt;String&gt;</code> and can resolve generic type parameters. Cortex knows that <code>foo</code> is a function that calls <code>bar</code> and is called by <code>baz</code>. For structural questions (callers, callees, blast radius, dead code), tree-sitter extraction is sufficient. For type-level questions, LSP is more accurate.</p>
<hr />
<h2>The tech stack in detail</h2>











































































































<table><thead><tr><th>Component</th><th>Crate / Technology</th><th>Version</th><th>Purpose</th></tr></thead><tbody><tr><td>CLI</td><td><code>clap</code> (derive macros)</td><td>4.x</td><td>Argument parsing, subcommand routing</td></tr><tr><td>Database</td><td><code>rusqlite</code> (bundled)</td><td>0.32</td><td>SQLite with WAL, FTS5, compiled from source</td></tr><tr><td>Serialization</td><td><code>serde</code> + <code>serde_json</code></td><td>1.x</td><td>JSON-RPC protocol, bundle format, config</td></tr><tr><td>Parsing</td><td><code>tree-sitter</code> + 26 grammar crates</td><td>0.25</td><td>AST extraction for 26 languages</td></tr><tr><td>Parallelism</td><td><code>rayon</code></td><td>1.x</td><td>Work-stealing thread pool for file parsing</td></tr><tr><td>Async runtime</td><td><code>tokio</code> (full features)</td><td>1.x</td><td>MCP server, concurrent tool handling</td></tr><tr><td>File watching</td><td><code>notify</code></td><td>7.x</td><td>Native OS filesystem events</td></tr><tr><td>Hashing</td><td><code>sha2</code></td><td>0.10</td><td>Content-based change detection</td></tr><tr><td>File walking</td><td><code>walkdir</code></td><td>2.x</td><td>Recursive directory traversal with .gitignore</td></tr><tr><td>Pattern matching</td><td><code>regex</code></td><td>1.x</td><td>Security pattern detection, taint source/sink matching</td></tr><tr><td>Error handling</td><td><code>anyhow</code> + <code>thiserror</code></td><td>1.x / 2.x</td><td>Application errors vs. typed library errors</td></tr><tr><td>Logging</td><td><code>tracing</code> + <code>tracing-subscriber</code></td><td>0.1 / 0.3</td><td>Structured logging with env-filter and JSON output</td></tr><tr><td>Config</td><td><code>toml</code></td><td>0.8</td><td><code>.cortex/config.toml</code> parsing</td></tr><tr><td>IDs</td><td><code>uuid</code> (v4)</td><td>1.x</td><td>Observation and ADR identifiers</td></tr><tr><td>HTTP server</td><td><code>axum</code> + <code>tower-http</code> (optional)</td><td>0.7 / 0.5</td><td>Visualizer endpoint, CORS</td></tr><tr><td>ML inference</td><td><code>ort</code> + <code>tokenizers</code> + <code>ndarray</code> (optional)</td><td>2.0-rc / 0.21 / 0.16</td><td>ONNX runtime for semantic embeddings</td></tr></tbody></table>
<p>The <code>bundled</code> feature on <code>rusqlite</code> means SQLite itself is compiled from C source and statically linked. This prevents system SQLite version conflicts, and the binary works on a fresh OS install with nothing else installed.</p>
<p>Optional features are gated behind Cargo feature flags. <code>--features visualizer</code> enables the axum HTTP server for the 3D graph UI. <code>--features semantic</code> enables ONNX inference for vector search. The default build includes neither, keeping the binary size around 25 MB with all 26 tree-sitter grammars statically linked.</p>
<hr />
<h2>Performance numbers</h2>
<p>These are measured values from actual usage, not theoretical estimates:</p>
















































































<table><thead><tr><th>What</th><th>Measured</th><th>Context</th></tr></thead><tbody><tr><td>Full index, 127 files, ~30K lines</td><td>535ms</td><td>Typical web application</td></tr><tr><td>Full index, 3,500 files (CPython stdlib)</td><td>&lt;60s</td><td>Large Python project</td></tr><tr><td>Incremental re-index, no changes</td><td>13ms</td><td>Hash comparison only</td></tr><tr><td>Incremental re-index, 1 file changed</td><td>&lt;15ms</td><td>Single file re-parse + write</td></tr><tr><td><code>trace_callers</code> query, depth 3</td><td>&lt;5ms</td><td>BFS over indexed edges</td></tr><tr><td><code>get_architecture</code> response size</td><td>~1,000 tokens</td><td>Regardless of codebase size</td></tr><tr><td><code>get_file_context</code> response size</td><td>500-800 tokens</td><td>vs. 15,000+ tokens for raw file</td></tr><tr><td>Token reduction on structural queries</td><td>100x</td><td>200 tokens vs. 20,000 tokens</td></tr><tr><td>Binary size, release build, stripped</td><td>~25 MB</td><td>All grammars statically linked</td></tr><tr><td>Database size, 127-file project</td><td>~2 MB</td><td>Nodes + edges + FTS5 index</td></tr><tr><td>First build from source</td><td>3-5 minutes</td><td>Compiling all tree-sitter C sources</td></tr><tr><td>Incremental Rust build</td><td>20-40 seconds</td><td>After initial compilation</td></tr><tr><td>MCP server startup</td><td>&lt;100ms</td><td>Database open + schema check</td></tr><tr><td>Concurrent read connections</td><td>1-16 (default 4)</td><td>Configurable via pool_size</td></tr></tbody></table>
<hr />
<h2>Full feature comparison</h2>
<p>This table compares Cortex against every relevant tool in the space based on what each tool actually ships today, not roadmap items:</p>






























































































































































































































<table><thead><tr><th>Feature</th><th>Cortex</th><th>LeanCTX</th><th>codebase-memory-mcp</th><th>Repomix</th></tr></thead><tbody><tr><td>Architecture</td><td>Rust binary, SQLite</td><td>Rust binary</td><td>C binary, SQLite</td><td>Node.js CLI</td></tr><tr><td>Languages</td><td>29</td><td>21</td><td>155</td><td>N/A</td></tr><tr><td>MCP tools</td><td>32 (or 5 smart)</td><td>59</td><td>14</td><td>0</td></tr><tr><td>Smart routing</td><td>Yes</td><td>No</td><td>No</td><td>N/A</td></tr><tr><td>Call graph tracing</td><td>BFS depth 5</td><td>Partial</td><td>BFS depth 5</td><td>No</td></tr><tr><td>HTTP linking</td><td>Yes</td><td>Yes</td><td>Yes</td><td>No</td></tr><tr><td>Dead code</td><td>Yes</td><td>No</td><td>Yes</td><td>No</td></tr><tr><td>Taint flow</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>OWASP scan</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>SBOM generation</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Dependency check</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Cross-session memory</td><td>Yes</td><td>Yes</td><td>No</td><td>No</td></tr><tr><td>Staleness invalidation</td><td>Yes</td><td>Yes</td><td>No</td><td>No</td></tr><tr><td>Multi-repo federation</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Hybrid search</td><td>Yes</td><td>Yes</td><td>Graph only</td><td>No</td></tr><tr><td>CI quality gates</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>3D visualization</td><td>Yes</td><td>No</td><td>Yes</td><td>No</td></tr><tr><td>Git hotspots</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Coverage gap analysis</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Community detection</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Build system workspaces</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Shell output compression</td><td>No</td><td>Yes</td><td>No</td><td>No</td></tr><tr><td>Delta reads</td><td>No</td><td>Yes</td><td>Partial</td><td>No</td></tr><tr><td>Token dashboard</td><td>No</td><td>Yes</td><td>No</td><td>Partial</td></tr><tr><td>Session resume</td><td>No</td><td>Yes</td><td>No</td><td>No</td></tr><tr><td>Single binary, zero deps</td><td>Yes</td><td>Yes</td><td>Yes</td><td>No</td></tr><tr><td>Auto IDE config</td><td>25 agents</td><td>28 agents</td><td>8 agents</td><td>N/A</td></tr><tr><td>Portable bundle</td><td>Yes</td><td>No</td><td>No</td><td>Yes</td></tr><tr><td>CLAUDE.md generation</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>License</td><td>MIT</td><td>MIT + Apache 2.0</td><td>MIT</td><td>MIT</td></tr></tbody></table>
<p>Cortex is strongest compared to the field in security analysis, staleness-aware memory, CI quality gates, coverage gap analysis, and the combination of graph intelligence with zero-dependency deployment.</p>
<p>Cortex is weaker in shell output compression (LeanCTX’s strongest feature), delta reads for repeated file access, token savings dashboards, and supporting fewer languages than codebase-memory-mcp.</p>
<hr />
<h2>Specific combinations that create compounding value</h2>
<p>Individual features are table stakes. The real engineering value comes from specific combinations that no single competitor offers in one binary:</p>
<ul>
<li><strong>Graph intelligence + security analysis + CI gates:</strong> Cortex is the only tool that can answer “what calls this function?”, “does user input reach this SQL query?”, and “fail the build if taint flows exist” from the same graph in the same binary. Running <code>cortex ci --fail-on-taint</code> in a GitHub Actions workflow means every PR gets structural security analysis without configuring heavy third-party enterprise security tooling.</li>
<li><strong>Cross-session memory + staleness invalidation + ADRs:</strong> No other tool combines persistent agent memory with automatic trust degradation. This combination means an agent that has worked on your codebase for months builds genuine institutional knowledge that degrades gracefully instead of becoming silently wrong.</li>
<li><strong>Federation + HTTP linking + blast radius:</strong> For microservice architectures, this combination answers “if I change this endpoint in service A, what breaks in services B, C, and D?” in one tool call across repository boundaries.</li>
<li><strong>Leiden community detection + build system awareness + hotspot analysis:</strong> This combination produces a structural health report that would take a senior architect a week to assemble manually. You can see your actual module boundaries, where they diverge from intended boundaries, and where the highest-risk code lives, in one command, with zero LLM cost.</li>
<li><strong>Smart tool routing + token budget management + task context extraction:</strong> The agent describes its task. Cortex returns exactly the relevant subgraph sized to fit the agent’s remaining context budget. The agent starts working with full structural awareness without having read a single file.</li>
</ul>
<hr />
<h2>Real usage patterns</h2>
<p>Here is what using Cortex looks like in practice across different workflows.</p>
<h3>Refactoring a legacy module</h3>
<p>Before touching anything, understand the impact:</p>
<pre><code>cortex impact LegacyAuth.validateSession --depth 5

# Output: 47 functions across 12 files depend on this
# Risk: 3 taint paths flow through this function
# Hotspot score: 340 (changed 17 times in 6 months, 20 callers)

# Check what the agent remembers about this code
cortex memory show
# Output: 2 observations (1 stale), 1 ADR about the auth migration plan

# Start the refactoring session with full context
cortex serve --smart-tools
# Agent asks: "explain LegacyAuth.validateSession"
# Cortex returns: callers, callees, observations, security flags in ~800 tokens
</code></pre>
<h3>Onboarding to an unfamiliar codebase</h3>
<pre><code>cortex index                    # 535ms for a typical project
cortex report                   # generates CORTEX_REPORT.md with full architecture overview
cortex viz --export graph.html  # visual map of the codebase structure
cortex modules                  # shows module boundaries and coupling scores

# In your agent session:
# "What is the architecture of this project?"
# Cortex returns: languages, entry points, module structure, ~1000 tokens
# vs. the agent reading 20+ files to figure this out
</code></pre>
<h3>Security audit before a release</h3>
<pre><code>cortex security scan            # taint flows + OWASP patterns
cortex security vulns           # dependency CVEs from OSV.dev
cortex ci --fail-on-taint --fail-on-owasp --format json &gt; security-report.json

# In CI (GitHub Actions):
# - name: Security gate
#   run: cortex ci --fail-on-taint --fail-on-owasp
# Exit code 1 blocks the merge if issues exist
</code></pre>
<h3>Microservice architecture analysis</h3>
<pre><code>cortex federate add ../user-service
cortex federate add ../payment-service
cortex federate add ../notification-service

# Now queries span all services
# "What calls PaymentService.processRefund?"
# Returns callers from user-service AND notification-service

# "What HTTP routes exist across all services?"
# Returns unified route map with cross-service links
</code></pre>
<h3>Finding coverage gaps that matter</h3>
<pre><code>cortex coverage --lcov coverage.lcov --limit 20

# Output ranked by risk:
# 1. db::connection_pool::acquire  | 0% covered | 47 callers
# 2. auth::token::refresh          | 0% covered | 31 callers
# 3. api::middleware::rate_limit   | 0% covered | 28 callers
# ...
# These are the functions where a bug would affect the most code
</code></pre>
<hr />
<h2>Configuration and tuning</h2>
<p>Cortex reads configuration from environment variables (prefix <code>CORTEX_</code>) and a configuration file at <code>.cortex/config.toml</code> in the repository root. Environment variables override file values.</p>
<pre><code># .cortex/config.toml - all fields optional, defaults shown
repo_root = "."
data_dir = ".cortex"
log_level = "info"
max_traversal_depth = 5          # max BFS depth for callers/callees/blast_radius
max_graph_query_results = 500    # cap on query results
auto_index = true                # re-index on file changes
update_check = true              # check for new versions on startup
auto_bundle_export = true        # export cortex.json after each index
pool_size = 4                    # read connections (1-16)
additional_repos = []            # paths for multi-repo federation
</code></pre>
<p>For most projects, the defaults work without any configuration file. The only tuning most developers do is increasing <code>pool_size</code> if they have multiple agents querying simultaneously, or setting <code>additional_repos</code> for federation.</p>
<hr />
<h2>Supported platforms (all 25)</h2>







































































































































<table><thead><tr><th>Platform</th><th>Install command</th><th>Config location</th></tr></thead><tbody><tr><td>Claude Code (Linux/Mac)</td><td><code>cortex install</code></td><td><code>~/.claude/settings.json</code></td></tr><tr><td>Claude Code (Windows)</td><td><code>cortex install --platform claude-code</code></td><td><code>%APPDATA%\Claude\claude_desktop_config.json</code></td></tr><tr><td>Cursor</td><td><code>cortex cursor install</code></td><td><code>~/.cursor/mcp.json</code></td></tr><tr><td>VS Code Copilot Chat</td><td><code>cortex vscode install</code></td><td><code>.vscode/mcp.json</code></td></tr><tr><td>GitHub Copilot CLI</td><td><code>cortex install --platform copilot</code></td><td><code>~/.config/github-copilot/mcp.json</code></td></tr><tr><td>Windsurf</td><td><code>cortex install --platform windsurf</code></td><td><code>~/.codeium/windsurf/mcp_config.json</code></td></tr><tr><td>Kiro IDE</td><td><code>cortex kiro install</code></td><td><code>~/.kiro/settings/mcp.json</code></td></tr><tr><td>Zed</td><td><code>cortex install --platform zed</code></td><td><code>~/.config/zed/settings.json</code></td></tr><tr><td>JetBrains</td><td><code>cortex install --platform jetbrains</code></td><td><code>~/.config/github-copilot/mcp.json</code></td></tr><tr><td>Cline/Roo</td><td><code>cortex install --platform cline</code></td><td><code>.cline/mcp.json</code></td></tr><tr><td>OpenAI Codex</td><td><code>cortex install --platform codex</code></td><td><code>~/.codex/mcp.json</code></td></tr><tr><td>OpenCode</td><td><code>cortex install --platform opencode</code></td><td>detected automatically</td></tr><tr><td>OpenClaw</td><td><code>cortex install --platform openclaw</code></td><td>detected automatically</td></tr><tr><td>Factory Droid</td><td><code>cortex install --platform droid</code></td><td>detected automatically</td></tr><tr><td>Trae</td><td><code>cortex install --platform trae</code></td><td>detected automatically</td></tr><tr><td>Trae CN</td><td><code>cortex install --platform trae-cn</code></td><td>detected automatically</td></tr><tr><td>Gemini CLI</td><td><code>cortex install --platform gemini</code></td><td>detected automatically</td></tr><tr><td>Hermes</td><td><code>cortex install --platform hermes</code></td><td>detected automatically</td></tr><tr><td>Kimi Code</td><td><code>cortex install --platform kimi</code></td><td>detected automatically</td></tr><tr><td>Pi coding agent</td><td><code>cortex install --platform pi</code></td><td>detected automatically</td></tr><tr><td>Google Antigravity</td><td><code>cortex antigravity install</code></td><td>detected automatically</td></tr><tr><td>Aider</td><td><code>cortex install --platform aider</code></td><td>detected automatically</td></tr><tr><td>Continue.dev</td><td><code>cortex install --platform continue</code></td><td>detected automatically</td></tr><tr><td>Supermaven</td><td><code>cortex install --platform supermaven</code></td><td>detected automatically</td></tr><tr><td>Tabnine</td><td><code>cortex install --platform tabnine</code></td><td>detected automatically</td></tr></tbody></table>
<p>The <code>install</code> command is idempotent. Running it again does not duplicate configuration; it merges the Cortex MCP server entry into existing config files without overwriting other settings.</p>
<hr />
<h2>What the future looks like</h2>
<p>Cortex 1.0 shipped in May 2026. The roadmap from here is informed by what the competitive landscape validates as high-value and what Cortex’s architecture makes uniquely possible.</p>
<p><strong>Near-term (already in progress):</strong></p>
<ul>
<li>Kotlin tree-sitter support (waiting for upstream updates to resolve version conflicts with older grammars).</li>
<li>More granular taint propagation (tracking data flow through struct fields, not just function boundaries).</li>
<li>Incremental bundle export (diff-based updates instead of full serialization).</li>
</ul>
<p><strong>Medium-term:</strong></p>
<ul>
<li><strong>Live collaboration mode:</strong> Multiple agents querying the same Cortex instance simultaneously with conflict-free observation writes.</li>
<li><strong>Graph diffing between branches:</strong> Not just “what files changed” but “what structural relationships changed” between <code>main</code> and a feature branch.</li>
<li><strong>Custom tree-sitter queries:</strong> Let users define their own extraction patterns for domain-specific constructs (e.g., extracting GraphQL resolvers, React component props, database migration steps).</li>
</ul>
<p><strong>Long-term:</strong></p>
<ul>
<li><strong>Distributed federation:</strong> Query across repositories on different machines (currently federation requires local filesystem access).</li>
<li><strong>Temporal graph:</strong> Track how the call graph evolves over time, not just its current state. “When did this function gain 20 new callers?” “When did this module become coupled to that one?”</li>
<li><strong>Agent coordination:</strong> When multiple agents work on the same codebase, Cortex could mediate their observations and flag conflicts.</li>
</ul>
<p>The core thesis does not change: agents need structure, not text. As models get larger context windows, the token savings become less about fitting within limits and more about signal-to-noise ratio. A 200-token graph result is not just cheaper than a 20,000-token file dump. It is also cleaner. The agent does not have to parse irrelevant code to find the structural answer.</p>
<hr />
<h2>Try it</h2>
<pre><code># Install (downloads binary, detects your agents, writes MCP config)
npx @1337xcode/cortex install

# Index your repository
cortex index

# Start using it - ask your agent structural questions
# "What calls processOrder?"
# "What breaks if I change DatabasePool.acquire?"
# "Show me the security findings"
# "What are the module boundaries?"
# "Find dead code in this project"
</code></pre>
<hr />
<h2>Closing thoughts</h2>
<p>The AI coding agent space in 2026 is crowded with model improvements, prompt engineering techniques, and context window expansions. Most of that work happens at the model layer or the prompt layer. Almost nobody is working seriously on the data layer, the question of what information the agent actually receives and in what form.</p>
<p>Repomix gives agents everything at once. LeanCTX compresses what agents receive. Engram intercepts and summarizes. Context7 injects documentation. Each approach has merit. Cortex takes a different position: it pre-computes the structural relationships that agents need most frequently and serves them as compressed, queryable, persistent knowledge.</p>
<p>The problem Cortex solves is prominent but undertouched. Agents are memory-constrained like Jolyne under Jail House Lock. The solution is engineering, not bigger models. Give the agent a mirror that shows all the bullets at once instead of making it memorize them one by one.</p>
<p>The code is open. The license is MIT. The binary is free. If you are building AI coding tools, working with AI coding agents daily, or just tired of watching your agent burn 50,000 tokens to answer a question that should cost 200, give it a try. The graph does not lie.</p>
<div><div><div></div><div>NOTE</div></div><div><p>Cortex is open source and licensed under the MIT license. The source code, npm package, and documentation are available on <a href="https://github.com/1337Xcode/cortex" rel="noopener noreferrer" target="_blank">GitHub</a>.</p></div></div>
<hr />
<h2>Further reading</h2>
<ul>
<li><a href="https://modelcontextprotocol.io/" rel="noopener noreferrer" target="_blank">Model Context Protocol Specification</a> - The official Model Context Protocol specification and documentation.</li>
<li><a href="https://arxiv.org/abs/2408.03910" rel="noopener noreferrer" target="_blank">CodexGraph: Bridging Large Language Models and Code Repositories via Code Graph Databases</a> (Liu et al., 2024) - The academic work most aligned with Cortex’s core approach: extracting code graphs and querying them via structured interfaces rather than file reading.</li>
<li><a href="https://arxiv.org/abs/2406.07003" rel="noopener noreferrer" target="_blank">GraphCoder: Enhancing Repository-Level Code Completion via Code Context Graph-based Retrieval and Language Model</a> (Liu et al., 2024) - Graph-based RAG for code completion showing +6.06 exact match improvement over sequence-based retrieval baselines.</li>
<li><a href="https://research.trychroma.com/context-rot" rel="noopener noreferrer" target="_blank">Context Rot: How Increasing Input Tokens Impacts LLM Performance</a> (Chroma Research, 2025) - 18 frontier models, all showing measurable performance degradation as input length grows. The empirical case for why raw file reading hurts agent quality.</li>
<li><a href="https://arxiv.org/abs/2510.05381" rel="noopener noreferrer" target="_blank">Context Length Alone Hurts LLM Performance Despite Perfect Retrieval</a> (2025) - Evidence that even with perfect retrieval, longer context degrades LLM output quality, strengthening the case for minimal, structured inputs.</li>
<li><a href="https://repositum.tuwien.at/bitstream/20.500.12708/224666/1/Hrubec%20Nicolas%20-%202025%20-%20Reducing%20Token%20Usage%20of%20Software%20Engineering%20Agents.pdf" rel="noopener noreferrer" target="_blank">Reducing Token Usage of Software Engineering Agents</a> (TU Wien, 2025) - Academic treatment of context management for software engineering agents, directly relevant to what Cortex addresses at the engineering layer.</li>
</ul>]]></content:encoded>
      <category>AI Agents</category>
      <category>Rust</category>
      <category>MCP</category>
    </item>
    <item>
      <title>PersonaBot: Building a Reliable RAG Assistant</title>
      <link>https://www.darshanchheda.com/posts/personabot</link>
      <guid isPermaLink="true">https://www.darshanchheda.com/posts/personabot</guid>
      <pubDate>Sat, 18 Apr 2026 00:00:00 GMT</pubDate>
      <updated>2026-04-18T00:00:00.000Z</updated>
      <dc:creator>Darshan Chheda</dc:creator>
      <description><![CDATA[How I built PersonaBot as a production system with staged routing, hybrid retrieval and reranking, bounded retries, SSE streaming, and weekly eval gates with automatic chunk cleanup.]]></description>
      <content:encoded><![CDATA[<img src="https://www.darshanchheda.com/_astro/rag.D4M8FZ3d.jpeg" alt="PersonaBot: Building a Reliable RAG Assistant" style="width: 100%; height: auto; margin-bottom: 1em;" />
<p>Most portfolio assistants fail in the same place. They can answer broad questions, but they break on specific ones. They also make it hard to tell when they are wrong.</p>
<p>I built PersonaBot to avoid that. The project is a retrieval-first system with explicit routing, confidence gates, source-linked answers, and an evaluation loop that runs in production workflows.</p>
<h2>System goals and constraints</h2>
<p>The design started with practical constraints.</p>
<ol>
<li>Answers must be grounded in indexed sources.</li>
<li>The route for each request should be predictable and debuggable.</li>
<li>Latency should stay stable under free tier limits.</li>
<li>Every stage should emit enough data for offline analysis.</li>
</ol>
<p>That is why the project is structured as a staged pipeline rather than one large model call.</p>
<h2>Runtime architecture</h2>
<img src="https://www.darshanchheda.com/_astro/architecture.BW8Nqf3f.png" alt="Runtime architecture diagram" />
<p>Each layer has a narrow responsibility.</p>
<ol>
<li>The Worker handles edge origin checks and coarse rate limiting.</li>
<li>FastAPI owns auth, SSE streaming, and service wiring at startup.</li>
<li>LangGraph controls routing with typed state transitions.</li>
<li>Retrieval and generation services stay stateless and replaceable.</li>
</ol>
<p>Startup wiring in <code>backend/app/main.py</code> is also important. Shared clients are initialized once in lifespan. They are not recreated per request. That removes a lot of avoidable latency variance.</p>
<h2>Ingestion and indexing</h2>
<p>The ingestion pipeline does more than chunk and embed.</p>
<ol>
<li>Parses blog posts, projects, PDF resume content, and public README sources.</li>
<li>Chunks content by heading and tags each chunk as <code>leaf</code>.</li>
<li>Extracts keyword payload fields for exact entity filtering.</li>
<li>Stores dense and sparse vectors on the same Qdrant point.</li>
<li>Adds <code>question_proxy</code> points for retrieval recall.</li>
<li>Builds RAPTOR summary nodes as a separate stage.</li>
</ol>
<pre><code>for chunk in chunks:
    chunk["metadata"]["chunk_type"] = "leaf"
    chunk["metadata"]["keywords"] = _extract_keywords(chunk["text"])

dense_embeddings = await embedder.embed(contextualised_texts, is_query=False)
sparse_embeddings = sparse_encoder.encode([c["text"].lower() for c in chunks])
leaf_uuids = store.upsert_chunks(chunks, dense_embeddings, sparse_embeddings)
</code></pre>
<p>Dense vectors use <code>BAAI/bge-small-en-v1.5</code>. Sparse vectors use BM25 through FastEmbed. This combination helps with both semantic questions and exact name matching.</p>
<p>In GitHub ingestion mode, the collection can be force recreated to avoid stale artifacts from renamed or deleted content.</p>
<h2>Request lifecycle stage by stage</h2>
<p>The request path is explicit in the graph.</p>
<img src="https://www.darshanchheda.com/_astro/request.B3uYvRW3.png" alt="Request lifecycle diagram" />
<h3>Stage 1. Guard and sanitization</h3>
<p>The pipeline sanitizes input first, then redacts PII patterns, then runs scope classification.</p>
<p>The classifier path is DistilBERT when artifacts exist. It falls back to regex rules when model artifacts are absent. The threshold is <code>0.70</code> with tokenizer <code>max_length=128</code>.</p>
<pre><code>inputs = self._tokenizer(text, return_tensors="pt", truncation=True, padding=True, max_length=128)
is_in_scope = in_scope_prob &gt;= 0.70
</code></pre>
<h3>Stage 2. Enumeration query branch</h3>
<p>List intent is handled before cache and before retrieval embeddings.</p>
<p>If the query asks for a complete list, the node scrolls Qdrant by payload filter and returns a deduplicated, title-level set. This avoids partial lists that can happen with similarity top-k retrieval.</p>
<h3>Stage 3. Semantic cache</h3>
<p>Cache lookup happens before expensive retrieval and generation.</p>
<p>Configured values in <code>backend/app/core/config.py</code> are below.</p>
<pre><code>SEMANTIC_CACHE_SIZE: int = 512
SEMANTIC_CACHE_TTL_SECONDS: int = 3600
SEMANTIC_CACHE_SIMILARITY_THRESHOLD: float = 0.92
</code></pre>
<p>The cache also stores query embeddings in state so the retrieve node can reuse them and avoid duplicate embed calls.</p>
<h3>Stage 4. Gemini fast path and query preparation</h3>
<p>Gemini can answer trivial conversational queries directly. Non trivial and entity specific portfolio queries route to full RAG.</p>
<p>At request entry, two best-effort tasks are started in parallel.</p>
<ol>
<li>Decontextualize follow-up phrasing into a standalone query.</li>
<li>Expand query forms for canonical names and related terms.</li>
</ol>
<p>Budgets are short so they do not slow first token.</p>
<pre><code>_DECONTEXT_TIMEOUT_SECONDS: float = 0.35
_EXPANSION_TIMEOUT_SECONDS: float = 0.60
_SSE_HEARTBEAT_SECONDS: float = 10.0
</code></pre>
<h3>Stage 5. Hybrid retrieval and reranking</h3>
<p>Retrieve combines three candidate streams.</p>
<ol>
<li>Dense vector search.</li>
<li>Sparse BM25 search.</li>
<li>Keyword payload filter search.</li>
</ol>
<p>Then it fuses ranks with RRF and expands sibling chunks by <code>doc_id</code> before reranking.</p>
<img src="https://www.darshanchheda.com/_astro/retrieval_reranking.CvvA0VEV.png" alt="Retrieval and reranking diagram" />
<p>Core gate constants in <code>backend/app/pipeline/nodes/retrieve.py</code>.</p>
<pre><code>_MIN_TOP_SCORE: float = -3.5
_MIN_RESCUE_SCORE: float = -6.0
_CRAG_LOW_CONFIDENCE_SCORE: float = -1.5
_RRF_K: int = 60
_SIBLING_EXPAND_TOP_N: int = 10
_SIBLING_FETCH_LIMIT: int = 20
_SIBLING_TOTAL_CAP: int = 15
</code></pre>
<p>Reranker service calls are retried once on transient errors.</p>
<pre><code>@retry(
    stop=stop_after_attempt(2),
    wait=wait_exponential(multiplier=0.4, min=0.4, max=1.2),
    retry=retry_if_exception_type((httpx.TimeoutException, httpx.HTTPError)),
    reraise=True,
)
async def _remote_call() -&gt; tuple[list[int], list[float]]:
    async with httpx.AsyncClient(timeout=60.0) as client:
        ...
</code></pre>
<p>Diversity caps are applied after rerank so one long document does not dominate the final context window.</p>
<h3>Stage 6. Rewrite retry (CRAG style)</h3>
<p>When retrieval is weak, the pipeline rewrites and retries instead of generating immediately.</p>
<p>The graph allows one retry for all meaningful queries and can allow a second retry for portfolio relevant noun queries. Retry count is tracked in state to keep the loop bounded.</p>
<h3>Stage 7. Generation and citation handling</h3>
<p>Generation uses Groq models selected by complexity.</p>
<ol>
<li>Default model is <code>llama-3.1-8b-instant</code>.</li>
<li>Large model is <code>llama-3.3-70b-versatile</code>.</li>
</ol>
<p>A shared TPM bucket prevents hard rate-limit failures by downgrading large model calls when usage in the current 60 second window passes the configured threshold.</p>
<pre><code>class TpmBucket:
    _WINDOW_SECONDS: int = 60
    _DOWNGRADE_THRESHOLD: int = 12_000
</code></pre>
<p>Response handling in <code>generate.py</code> is strict.</p>
<ol>
<li>Stream tokens.</li>
<li>Strip <code>&lt;think&gt;</code> traces.</li>
<li>Normalize and reindex citations.</li>
<li>Deduplicate source cards by URL identity.</li>
<li>Trigger low-trust fallback behavior when needed.</li>
</ol>
<h3>Stage 8. Streaming contract and follow-ups</h3>
<p>The API streams typed SSE events such as <code>status</code>, <code>reading</code>, <code>sources</code>, <code>thinking</code>, <code>token</code>, <code>follow_ups</code>, and final <code>done</code>.</p>
<p>Follow-up questions are generated after the main answer stream finishes. This keeps answer latency stable.</p>
<h3>Stage 9. Logging and interaction schema</h3>
<p>Every path writes to SQLite through <code>log_eval</code>.</p>
<p>Logged fields include query, answer, reranked chunk IDs, rerank scores, latency, path label, critic scores, enumeration flag, and retrieval diagnostics such as sibling expansion count.</p>
<p>That schema is what powers later evaluation and data prep workflows.</p>
<h2>Security and reliability</h2>
<p>Security is layered at edge, API, and pipeline level.</p>



































<table><thead><tr><th>Layer</th><th>Control</th><th>Verified behavior</th></tr></thead><tbody><tr><td>Edge</td><td>Cloudflare Worker</td><td>origin controls plus 30 req/min/IP global limit</td></tr><tr><td>Edge audio</td><td>Cloudflare Worker</td><td>10 req/min/IP for <code>/transcribe</code></td></tr><tr><td>API</td><td>slowapi limiter</td><td>20 req/min on chat endpoint</td></tr><tr><td>Auth</td><td>JWT validation</td><td>bearer token required on protected routes</td></tr><tr><td>Input</td><td>sanitizer + guard</td><td>sanitize, redact, classify before retrieval/generation</td></tr></tbody></table>
<pre><code>if (entry.count &gt; 30) {
  return new Response(JSON.stringify({ error: 'Rate limit exceeded. Try again in a minute.' }), { status: 429 })
}

if (url.pathname.startsWith('/transcribe') &amp;&amp; audioEntry.count &gt; 10) {
  return new Response(JSON.stringify({ error: 'Audio rate limit exceeded. Try again in a minute.' }), { status: 429 })
}
</code></pre>
<p>Reliability controls are also explicit.</p>
<ol>
<li>SSE heartbeat every 10 seconds to keep long responses alive through proxies.</li>
<li>Qdrant keepalive loop with a six day interval to avoid idle expiry patterns.</li>
<li>Bounded timeouts around expansion and decontext tasks.</li>
<li>Retry wrappers around remote model calls that can fail transiently.</li>
</ol>
<h2>Evaluation and improvement loop</h2>
<p>Production quality is treated as an engineering loop, not a one-time benchmark.</p>
<img src="https://www.darshanchheda.com/_astro/evaluation.CdV-bSX1.png" alt="Evaluation and improvement loop diagram" />
<p>The offline evaluator in <code>eval/run_eval.py</code> runs golden questions against the live API endpoint and tracks both retrieval and answer metrics.</p>
<p>Regression thresholds are defined in code.</p>
<ol>
<li><code>faithfulness &gt;= 0.75</code></li>
<li><code>answer_relevancy &gt;= 0.70</code></li>
</ol>
<p>The weekly workflow can run with or without RAGAS scoring. Operational checks still run when RAGAS is disabled.</p>
<p>Self purge runs in the same weekly loop using <code>scripts/purge_bad_chunks.py</code>.</p>
<ol>
<li>Candidate document appears at least 5 times as top chunk.</li>
<li>Max top rerank score is at most <code>-2.5</code>.</li>
<li>No positive feedback exists for those interactions.</li>
</ol>
<p>Reranker data prep runs in a separate workflow and requires at least 100 new triplets by default before pushing dataset updates.</p>
<h2>How to build a similar system</h2>
<p>If you want to build this kind of assistant yourself, this order is the most practical.</p>
<ol>
<li>Start with ingestion and reliable metadata fields.</li>
<li>Build deterministic routing before tuning prompts.</li>
<li>Add hybrid retrieval before trying larger generation models.</li>
<li>Add citation post-processing and source filtering before polishing UI.</li>
<li>Add logs with stable schemas early.</li>
<li>Add eval and purge automation before calling it production.</li>
</ol>
<p>A lot of teams reverse this order. They spend time on generation style before retrieval quality is stable. That usually slows progress because debugging stays ambiguous.</p>
<h2>Design choices that paid off</h2>
<h3>Explicit routing instead of one big prompt</h3>
<p>I split the pipeline into nodes (guard, cache, fast path, retrieve, rewrite, generate) so behavior stayed inspectable. It was easier to debug because each failure had a clear location.</p>
<h3>Hybrid retrieval before model scaling</h3>
<p>Dense search alone missed exact entities, and keyword search alone missed intent. Running dense, sparse BM25, and payload filters together gave better recall, then reranking cleaned up precision.</p>
<h3>Retries with hard limits</h3>
<p>Rewrite-and-retry improved weak retrieval cases, but only with strict retry caps. That kept latency predictable and stopped pathological loops.</p>
<h3>Quality gates in the weekly loop</h3>
<p>Offline eval plus chunk-purge scripts turned quality into a maintenance task, not a one-off benchmark. If relevance or faithfulness drifts, it shows up quickly.</p>
<h2>Engineering details that mattered</h2>
<p>These were small decisions that had outsized impact in practice.</p>
<ol>
<li>Shared clients are initialized once in FastAPI lifespan, which reduced per-request setup overhead and latency variance.</li>
<li>A semantic cache with threshold <code>0.92</code> and TTL <code>3600</code> removed repeat work on common queries.</li>
<li>The TPM bucket in <code>llm_client.py</code> downgrades large-model calls when usage crosses <code>12_000</code> tokens per minute.</li>
<li>SSE heartbeat (<code>10s</code>) plus bounded decontext and expansion timeouts kept long responses stable behind proxies.</li>
</ol>
<h2>Further reading</h2>
<ul>
<li><a href="https://langchain-ai.github.io/langgraph/" rel="noopener noreferrer" target="_blank">LangGraph</a> - Graph-based state machine for deterministic LLM pipelines.</li>
<li><a href="https://fastapi.tiangolo.com/advanced/events/" rel="noopener noreferrer" target="_blank">FastAPI lifespan events</a> - Lifecycle hooks for shared client initialization and cleanup.</li>
<li><a href="https://qdrant.tech/documentation/concepts/hybrid-queries/" rel="noopener noreferrer" target="_blank">Hybrid Search with Dense and Sparse Vectors</a> - Combining semantic and keyword retrieval in one pipeline.</li>
<li><a href="https://plg.uwaterloo.ca/~gvcormac/cormacksigir09-rrf.pdf" rel="noopener noreferrer" target="_blank">Reciprocal Rank Fusion</a> - Rank fusion algorithm for combining multiple retrieval signals.</li>
<li><a href="https://arxiv.org/abs/2401.15884" rel="noopener noreferrer" target="_blank">CRAG: Corrective Retrieval Augmented Generation</a> - Rewrite-and-retry pattern for weak retrieval recovery.</li>
<li><a href="https://docs.ragas.io/" rel="noopener noreferrer" target="_blank">RAGAS: Retrieval-Augmented Generation Assessment</a> - Metrics framework for retrieval and generation quality.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/API/EventSource" rel="noopener noreferrer" target="_blank">Server-Sent Events (SSE)</a> - Streaming protocol for real-time token and status delivery.</li>
</ul>
<blockquote><p>Live demo: <a href="https://www.darshanchheda.com/chat" rel="noopener noreferrer" target="_blank">darshanchheda.com/chat</a></p></blockquote>]]></content:encoded>
      <category>AI Engineering</category>
      <category>LangGraph</category>
      <category>System Design</category>
    </item>
    <item>
      <title>AimBuddy: Building a 60 FPS on-device tracking and touch injection system</title>
      <link>https://www.darshanchheda.com/posts/assistive-vision</link>
      <guid isPermaLink="true">https://www.darshanchheda.com/posts/assistive-vision</guid>
      <pubDate>Sun, 15 Feb 2026 00:00:00 GMT</pubDate>
      <updated>2026-02-15T00:00:00.000Z</updated>
      <dc:creator>Darshan Chheda</dc:creator>
      <description><![CDATA[How I built a real-time Android vision system from scratch using YOLO, DeepSORT, and uinput.]]></description>
      <content:encoded><![CDATA[<img src="https://www.darshanchheda.com/_astro/yolo.nDkUslto.jpg" alt="AimBuddy: Building a 60 FPS on-device tracking and touch injection system" style="width: 100%; height: auto; margin-bottom: 1em;" />

<div><div><div></div><div>TIP</div></div><div><p>I have decided to open source AimBuddy. Everything discussed in this post, the full native pipeline, training scripts, and docs, is now freely available on <a href="https://github.com/1337Xcode/AimBuddy" rel="noopener noreferrer" target="_blank">GitHub</a>.</p></div></div>
<p>AimBuddy started as an experiment to see if a phone could run a full real-time vision pipeline entirely on-device. Screen capture, YOLO inference, multi-target tracking, and programmatic touch injection, all natively on a mobile GPU at 60 FPS with no PC tethering. It can, but the interesting problems weren’t where I expected them.</p>
<p>Running YOLO on a phone was the easy part. NCNN with Vulkan gives you GPU compute shaders and FP16 ALUs for free. The problems that actually ate months of dev time were in the glue between components. How do you keep latency honest when the SoC thermally throttles and your inference time doubles? How do you make a tracker that doesn’t flicker every time a detection disappears for a frame? How do you inject touch events that feel like a human input and not a machine gun?</p>
<p>This post covers the full technical stack with every design decision, actual code, and the problems that were painful to debug.</p>
<div><div><div></div><div>IMPORTANT</div></div><div><p>This is a research and educational project. All testing was done in controlled environments.</p></div></div>
<h2>What AimBuddy actually is</h2>
<p>There are two runtime modes, and the split between them is deliberate:</p>
<ul>
<li><strong>Visual Assist</strong> (no root required) runs screen capture, YOLO inference, target tracking, and an ESP overlay. Works on any Android 11+ device.</li>
<li><strong>Assisted Input</strong> (root required) adds low-latency touch injection via Linux <code>uinput</code> on top of the visual pipeline.</li>
</ul>
<p>Root failure doesn’t crash the app. If <code>/dev/uinput</code> isn’t available or the grab fails, the visual pipeline keeps running and the touch layer just never starts. This matters during development when you’re constantly switching between root and non-root test devices.</p>
<p>The stack is Kotlin + Jetpack Compose for the Android UI layer, and C++ via JNI for everything on the hot path. The inference model is yolo26n, a nano-sized single-class detector from the YOLO26 family, running on NCNN with Vulkan compute.</p>
<h2>The architecture</h2>
<figure><img src="https://www.darshanchheda.com/_astro/architecture.DxfiN8tb.png" alt="AimBuddy architecture" /><figcaption>Architecture diagram for the full AimBuddy pipeline</figcaption></figure>
<p>Four threads at runtime. The inference thread is pinned to the Cortex-X1 big core and the render thread to a Cortex-A78 core via <code>sched_setaffinity</code>. This is done through an RAII <code>ESP::Thread</code> wrapper that takes an affinity parameter at start:</p>
<pre><code>bool start(int cpuAffinity = -1) {
    cpuAffinity_ = cpuAffinity;
    int result = pthread_create(&amp;thread_, nullptr, threadEntry, this);
    // ...
}

// Inside threadEntry:
cpu_set_t cpuset;
CPU_ZERO(&amp;cpuset);
CPU_SET(thread-&gt;cpuAffinity_, &amp;cpuset);
sched_setaffinity(0, sizeof(cpu_set_t), &amp;cpuset);
</code></pre>
<p>Pinning to specific cores on a big.LITTLE SoC is not optional for consistent timing. Without affinity, the scheduler freely migrates the inference thread between fast and slow cores, and your inference time oscillates wildly. That variance breaks the adaptive crop controller, which relies on stable EMA measurements to make decisions.</p>
<p>The inference and render threads don’t share a lock for frames. Data flows through a lock-free SPSC ring buffer from capture to inference, and through a <code>std::mutex</code>-protected copy from inference to render. The aim loop reads from the tracker under its own mutex. There’s no single choke point.</p>
<h2>Capture: MediaProjection and HardwareBuffer</h2>
<p>Android’s MediaProjection API gives you a <code>VirtualDisplay</code> you can attach an <code>ImageReader</code> to. Each frame arrives as an <code>AHardwareBuffer</code>, which is a reference to GPU memory you can pass directly to native code without copying:</p>
<pre><code>AHardwareBuffer* buffer = AHardwareBuffer_fromHardwareBuffer(env, hardwareBuffer);
AHardwareBuffer_acquire(buffer);

ESP::Frame frame;
frame.hardwareBuffer = buffer;
frame.timestamp = timestamp;
frame.width = g_captureWidth;
frame.height = g_captureHeight;

if (!g_frameBuffer-&gt;push(frame)) {
    AHardwareBuffer_release(buffer);
    // drop count tracked in FrameBuffer for periodic telemetry
}
</code></pre>
<p>Capture runs at 1280x720. Full 1080p doubles the preprocessing cost for no detection benefit since the model input is only 256x256. The pixels you’d gain are thrown away during the center crop and resize anyway.</p>
<p>The ring buffer has 8 slots, giving about 200ms of buffering headroom at 40+ FPS capture. You need this slack because inference occasionally takes longer than a single frame period, and you can’t let the capture thread block.</p>
<p>One thing I got burned by early on was the <code>ImageReader</code> buffer count. It’s configured with 3 max images:</p>
<pre><code>constexpr int IMAGE_READER_MAX_IMAGES = 3;
</code></pre>
<p>With 2 buffers, if inference is holding one and capture is writing another, the producer stalls. That tanks you from 60+ FPS to a lumpy ~30. Three buffers breaks that deadlock. It’s a classic producer-consumer problem, and it’s annoying to debug because the symptom looks like slow inference when it’s actually a buffer allocation bottleneck.</p>
<h2>The inference loop: drain to latest</h2>
<p>The inference thread doesn’t process frames in order. It drains the ring buffer to the newest available frame every iteration, deliberately dropping stale work:</p>
<pre><code>if (g_frameBuffer &amp;&amp; g_frameBuffer-&gt;pop(frame)) {
    ESP::Frame newer;
    uint64_t drainedThisIteration = 0;
    while (g_frameBuffer-&gt;pop(newer)) {
        if (frame.hardwareBuffer) {
            AHardwareBuffer_release(frame.hardwareBuffer);
        }
        frame = newer;
        drainedThisIteration++;
    }
    // run inference on freshest frame only
}
</code></pre>
<p>If the GPU is slow and frames pile up, processing them in order means you’re always behind reality. Dropping frames to stay current feels smoother and produces better tracking because the tracker’s velocity estimates are based on real-time deltas, not stale data.</p>
<p>When the inference loop has no frames, it doesn’t busy-wait. It uses exponential backoff starting at 200 microseconds and topping out at 2ms:</p>
<pre><code>const auto sleepDuration = std::min(kNoFrameSleepMin * (1u &lt;&lt; noFrameBackoffLevel), kNoFrameSleepMax);
std::this_thread::sleep_for(sleepDuration);
if (noFrameBackoffLevel &lt; 4) ++noFrameBackoffLevel;
</code></pre>
<p>When a frame arrives, <code>noFrameBackoffLevel</code> resets to 0 so the loop immediately returns to tight polling. This keeps CPU usage low when idle without adding latency when frames are flowing.</p>
<p>I track both average and EMA inference time per window of 120 frames, and the telemetry logs to logcat:</p>
<pre><code>Pipeline stats: avg infer=7.2ms avg e2e=14.1ms ema infer=7.8ms ema e2e=15.3ms crop=352 drained=1 dropped_push=0
</code></pre>
<p>If <code>drained</code> is consistently &gt; 2 per window, something’s under pressure. If <code>dropped_push</code> is nonzero, the ring buffer is overflowing and you’re losing frames at the capture side.</p>
<h2>Adaptive crop: treating crop size as a control variable</h2>
<p>This is probably the most interesting optimization in the codebase. The center crop size going into inference is not fixed. It adjusts at runtime based on two pressure signals.</p>
<pre><code>const bool backlogPressure = (drainedThisIteration &gt; 0);
const bool latencyPressure = (emaInferMs &gt; kTargetCycleMs) || (emaEndToEndMs &gt; kE2ePressureMs);

if (latencyPressure || backlogPressure) {
    adaptiveCropSize = std::max(kMinAdaptiveCrop, adaptiveCropSize - kDownscaleStep);
} else if (adaptiveCropSize &lt; cachedCropSize) {
    adaptiveCropSize = std::min(cachedCropSize, adaptiveCropSize + kUpscaleStep);
}
</code></pre>
<p>Under load the crop shrinks quickly per iteration. When pressure clears it grows back slowly toward the FOV-derived target. The asymmetric step sizes prevent oscillation. Fast shrink, slow grow is the same idea behind TCP congestion control: respond to overload quickly but recover cautiously so you don’t immediately re-enter overload.</p>
<p>The crop size also adapts to the user’s configured FOV radius. When the FOV setting changes, the system recomputes the target crop by mapping FOV pixels through the screen-to-capture resolution ratio:</p>
<pre><code>int targetSize = static_cast&lt;int&gt;(fovRadius * 2.0f);
targetSize = std::max(256, std::min(targetSize, safeScreenWidth));
const float scaleToCapture = static_cast&lt;float&gt;(Config::CAPTURE_WIDTH) / static_cast&lt;float&gt;(safeScreenWidth);
int dynamicCropSize = static_cast&lt;int&gt;(targetSize * scaleToCapture);
</code></pre>
<p>This means a small FOV setting automatically gives you a smaller crop and faster inference. The adaptive controller then further adjusts within that range based on runtime pressure.</p>
<h2>NCNN and Vulkan: getting inference under 10ms</h2>
<p>NCNN is Tencent’s mobile inference framework. I use it instead of TFLite because it has first-class Vulkan support, which means I can run compute shaders on the GPU instead of the CPU. The difference is roughly 3x throughput and significantly less thermal output.</p>
<p>The NCNN configuration for Adreno GPUs:</p>
<pre><code>net.opt.use_vulkan_compute = true;
net.opt.use_fp16_packed = true;
net.opt.use_fp16_storage = true;
net.opt.use_fp16_arithmetic = true;
net.opt.use_packing_layout = true;
net.opt.lightmode = true;
net.opt.num_threads = 4;  // CPU fallback threads
</code></pre>
<p>FP16 packed + arithmetic is the important one for Adreno GPUs. They have native FP16 ALUs and you need all three flags to actually use them. Without them you’re doing FP32 compute and losing roughly half the throughput. The <code>lightmode</code> flag tells NCNN to release intermediate blob memory after each layer, which keeps the memory footprint under control.</p>
<p>The model input is 256x256, not the standard 640x640. The preprocessing chain from HardwareBuffer:</p>
<figure><img src="https://www.darshanchheda.com/_astro/preprocessing.HFf1m-Ol.png" alt="Preprocessing pipeline" /><figcaption>Preprocessing pipeline from HardwareBuffer to model input</figcaption></figure>
<pre><code>const float normVals[3] = {1/255.f, 1/255.f, 1/255.f};
input.substract_mean_normalize(nullptr, normVals);
</code></pre>
<p>One thing that bit me was model export format differences. Depending on how you export from Ultralytics, the NCNN blob names may or may not be present in the param file. I handle this with a name-first, index-fallback strategy:</p>
<pre><code>int ret = -1;
if (!useInputIndex_ &amp;&amp; !inputBlobName_.empty()) {
    ret = ex.input(inputBlobName_.c_str(), input);
}
if (ret != 0) {
    useInputIndex_ = true;
    ret = ex.input(0, input);  // index fallback
}
</code></pre>
<p>Once fallback is triggered, <code>useInputIndex_</code> is cached so the name path isn’t retried every frame.</p>
<h2>Training the model</h2>
<p>The model is yolo26n, a single-class detector. The training pipeline enforces <code>yolo26n.pt</code> as a hard contract in both <code>train.py</code> and <code>download_base_model.py</code>. Passing a different base model name errors out immediately:</p>
<pre><code>if base_model.name.lower() != "yolo26n.pt":
    print("ERROR: base_model must be yolo26n.pt for this repository contract")
    return 2
</code></pre>
<p>I enforce this because the NCNN export output filenames, the inference layer names, and the model input dimensions are all downstream assumptions. Swapping the base model breaks the contract silently if you let it through.</p>
<p>Training runs on Windows with Ultralytics + PyTorch. The dataset is frames extracted from screen recordings, auto-labeled with a pre-trained detector, then manually reviewed to fix mistakes.</p>
<figure><img src="https://www.darshanchheda.com/_astro/export.BVQqeVWu.png" alt="Export pipeline" /><figcaption>Model export pipeline from PyTorch to NCNN</figcaption></figure>
<figure><img src="https://www.darshanchheda.com/_astro/training_results.Br6Y4lbA.png" alt="Training results" /><figcaption>Training curves showing clean convergence with no overfitting</figcaption></figure>
<figure><img src="https://www.darshanchheda.com/_astro/pr_curve.DggbuP2w.png" alt="Precision-Recall curve" /><figcaption>Precision-Recall curve at 0.5 IOU threshold</figcaption></figure>
<figure><img src="https://www.darshanchheda.com/_astro/val_predictions.C7oPgwql.jpg" alt="Validation batch predictions" /><figcaption>Validation predictions showing detection across different poses and occlusion levels</figcaption></figure>
<h2>NMS and postprocessing</h2>
<p>YOLO outputs thousands of candidate boxes at multiple scales. Most overlap. NMS filters them to the best non-overlapping set by computing Intersection over Union between every pair and suppressing lower-confidence boxes that overlap above a threshold:</p>
<pre><code>float iou(const BBox&amp; a, const BBox&amp; b) {
    float x1 = std::max(a.left(), b.left());
    float y1 = std::max(a.top(), b.top());
    float x2 = std::min(a.right(), b.right());
    float y2 = std::min(a.bottom(), b.bottom());

    float inter = std::max(0.f, x2-x1) * std::max(0.f, y2-y1);
    return inter / (a.area() + b.area() - inter);
}
</code></pre>
<p>After NMS, coordinates are remapped from model crop-space back to screen-space. This remapping is where coordinate system bugs hide. Off-by-one errors in the crop offset calculation show up as boxes that are consistently shifted by a few pixels in one direction, and it’s infuriating to track down because the detection itself looks correct.</p>
<p>The postprocessor also handles both transposed and non-transposed NCNN output layouts, since the format changed between Ultralytics export versions.</p>
<h2>DeepSORT-style tracking</h2>
<p>Raw YOLO detections are noisy. Boxes jump a few pixels each frame, sometimes disappear for a frame or two during partial occlusion. Reacting directly to raw detections produces jittery output. The tracker smooths this into stable identities.</p>
<p>I use a DeepSORT-inspired matching cascade. Instead of matching all detections to all tracks simultaneously, tracks are processed in order of increasing age (younger first). This prevents old occluded tracks from stealing detections that belong to recently-confirmed targets:</p>
<pre><code>// Match tracks in order of increasing age (younger first)
for (int currentAge = 0; currentAge &lt;= maxAge; currentAge++) {
    for (int t = 0; t &lt; numTracks; t++) {
        if (trkMatched[t]) continue;
        if (track.age != currentAge) continue;
        // ... find best detection match
    }
}
</code></pre>
<p>The matching score is a weighted combination of three signals:</p>
<pre><code>float score = iou * 0.70f + centerScore * 0.22f + areaScore * 0.08f;
if (isLockedTrack) score += 0.06f;  // bias toward current lock
</code></pre>
<p>70% IoU, 22% center distance, 8% area similarity. The locked target gets a small bonus, which makes the system sticky to its current target without being so sticky that it ignores a clearly better match.</p>
<p>Before matching, there’s also a spatial gate. If a detection’s center is too far from the track’s predicted position, it’s rejected without computing IoU at all. This prevents a track on the left of the screen from matching a detection that appeared on the right.</p>
<p>The real-time <code>dt</code> measurement is critical. A fixed timestep assumption breaks on Android because scheduling jitter is real:</p>
<pre><code>float dt = 1.0f / 60.0f;  // default
if (m_lastUpdateNs &gt; 0 &amp;&amp; nowNs &gt; m_lastUpdateNs) {
    dt = static_cast&lt;float&gt;(nowNs - m_lastUpdateNs) / 1'000'000'000.0f;
    dt = AimbotMath::clamp(dt, 1.0f / 120.0f, 1.0f / 20.0f);
}
</code></pre>
<p>Clamping <code>dt</code> between 1/120 and 1/20 prevents velocity estimates from exploding when scheduling hiccups cause a long gap between updates.</p>
<figure><img src="https://www.darshanchheda.com/_astro/tracking.C27Byztf.png" alt="Track lifecycle state diagram" /><figcaption>Track lifecycle state transitions</figcaption></figure>
<p>One-frame spurious detections never reach CONFIRMED state, so they never influence the controller. Three matches at 60 FPS is 50ms, short enough to feel responsive but long enough to filter garbage. Tentative tracks that miss even one frame are immediately removed (they never proved themselves), while confirmed tracks get a grace period.</p>
<p>Target selection has hysteresis. The locked target needs to be beaten by a significant margin before a switch happens, and there’s a cooldown on switches. The lock also needs to have matured for at least a few frames before a switch is even considered:</p>
<pre><code>const bool cooldownReady = (m_switchCooldownFrames &lt;= 0);
const bool lockMatured = (m_lockFrameCount &gt;= 4);
bool canSwitch = cooldownReady &amp;&amp; lockMatured;
</code></pre>
<p>This prevents identity bouncing when two targets are at similar distances.</p>
<h2>Velocity estimation and prediction</h2>
<p>When a track goes unmatched, I predict where it should be using its EMA-smoothed velocity:</p>
<pre><code>P_new = P_old + v_old * dt
</code></pre>
<p>The velocity EMA has confidence-aware blending. High-confidence detections get more influence on the velocity estimate. Mature tracks (many consecutive matches) use a slightly faster blending factor because they’ve proven stable:</p>
<pre><code>const float conf = AimbotMath::clamp(detection.confidence, 0.0f, 1.0f);
const float maturity = AimbotMath::clamp(static_cast&lt;float&gt;(track.consecutiveMatches) / 8.0f, 0.0f, 1.0f);
const float dynamicSmoothing = AimbotMath::clamp(smoothing + (1.0f - conf) * 0.20f - maturity * 0.10f, 0.15f, 0.92f);
</code></pre>
<p>There’s also a sub-pixel wobble suppression gate. If the detection center moved less than 0.9px from the previous frame, the velocity is forced to zero. Without this, detector quantization noise creates phantom velocity on stationary targets, which makes the lead prediction drift.</p>
<p>Velocity resets on large spatial jumps. If a detection appears far from where the predicted track should be, it’s almost certainly a different target, not the same one teleporting. When this happens, the EMA and Kalman filter states are also reset so the filters don’t try to interpolate across the discontinuity.</p>
<h2>Aim control: three modes, a PD controller, and a lot of clamping</h2>
<p>The controller reads from the tracker with a validated settings snapshot:</p>
<pre><code>UnifiedSettings settingsSnapshot = g_settings;
settingsSnapshot.validate();
</code></pre>
<p>Shared settings can change mid-run from the ImGui menu on the render thread. A snapshot + validate gives each aim iteration a coherent, bounds-checked parameter set. Without this, you get undefined behavior from reading a struct that’s being partially written on another thread.</p>
<p>Three aim modes:</p>

























<table><thead><tr><th>Mode</th><th>Behavior</th><th>Best for</th></tr></thead><tbody><tr><td>Smooth</td><td>PD controller with convergence damping</td><td>General use, natural feel</td></tr><tr><td>Snap</td><td>Gain-capped proportional (never exceeds 82% of distance per frame)</td><td>Fast acquisition</td></tr><tr><td>Magnetic</td><td>Distance-proportional pull (gentle near, stronger far)</td><td>Precision, minimal overshoot</td></tr></tbody></table>
<p>All three modes enforce an invariant: the movement vector can never point away from the target. This sounds obvious but it’s easy to violate with a derivative term. The controller checks this at multiple points in the pipeline:</p>
<pre><code>// Never move away from the target direction
if (outX * dx &lt; 0.0f) outX = 0.0f;
if (outY * dy &lt; 0.0f) outY = 0.0f;
</code></pre>
<p>The smooth mode uses a PD controller. I killed the integral term entirely:</p>
<pre><code>u[n] = K_p * e[n] + K_d * (e[n] - e[n-1]) / dt
</code></pre>
<p>Integral windup is a real problem here. If the target is briefly occluded, the integral accumulates error during that period. When the target reappears you overshoot badly because the integral is trying to make up for all the “missed” time. PD without integral is more stable for a system where the target disappears unpredictably.</p>
<p>The smooth mode also has convergence damping: when the crosshair is close to the target, the proportional gain is squared and scaled down to a minimum of 20%. This prevents the characteristic oscillation you get from a fast PD controller at small error. Without it, the output bounces back and forth across the target at sub-pixel amplitude, which looks terrible at 60 FPS.</p>
<p>The derivative term has distance-dependent clamping:</p>
<pre><code>const float derivativeClamp = AimbotMath::clamp(distance * 0.18f + 5.0f, 5.0f, 20.0f);
derivativeX = AimbotMath::clamp(derivativeX, -derivativeClamp, derivativeClamp);
derivativeY = AimbotMath::clamp(derivativeY, -derivativeClamp, derivativeClamp);
</code></pre>
<p>At close range the clamp is tight so single-frame jitter can’t produce a large correction. At long range it opens up so the derivative can actually contribute to tracking moving targets.</p>
<h3>Motion-gated lead prediction</h3>
<p>The controller applies predictive lead based on the tracker’s velocity estimate, but only when the target is actually moving. There’s a three-part gate:</p>
<ol>
<li><strong>Distance gate</strong>: lead scales from zero at close range to full at long range. No lead at point-blank because you don’t need it.</li>
<li><strong>Confidence gate</strong>: lead scales with detection confidence. Low-confidence detections produce noisy velocity, so don’t trust them for prediction.</li>
<li><strong>Motion speed gate</strong>: lead only kicks in when the target is actually moving above a minimum speed threshold. This is the critical one, because without it stationary targets drift due to detector quantization noise being fed through the velocity estimator.</li>
</ol>
<h3>Jitter suppression and movement smoothing</h3>
<p>Small movements when already locked are suppressed with a quadratic ramp:</p>
<pre><code>if (m_isAiming) {
    const float moveMag = std::sqrt(moveX * moveX + moveY * moveY);
    if (moveMag &lt; 1.5f &amp;&amp; moveMag &gt; EPSILON) {
        const float jitterScale = moveMag / 1.5f;
        moveX *= jitterScale * jitterScale;
        moveY *= jitterScale * jitterScale;
    }
}
</code></pre>
<p>A 0.5px movement becomes 0.5 _ (0.5/1.5)^2 = 0.056px, essentially zero. A 1.4px movement becomes 1.4 _ (1.4/1.5)^2 = 1.22px, nearly unchanged. The quadratic curve gives a smooth transition between “kill this noise” and “let it through.”</p>
<p>Movement is also EMA-blended between frames and direction reversals under a small threshold are halved. On the first frame after touch-down, movement is dampened to prevent the initial acquisition from looking too snappy.</p>
<h3>Touch radius clamping</h3>
<p>The touch position is constrained to a circular region around the configured center:</p>
<pre><code>if (distFromCenterSq &gt; touchRadius * touchRadius) {
    const float distFromCenter = std::sqrt(distFromCenterSq);
    const float scale = touchRadius / distFromCenter;
    m_touchX = touchCenterX + distFromCenterX * scale;
    m_touchY = touchCenterY + distFromCenterY * scale;
}
</code></pre>
<p>If the accumulated touch position drifts too far from center, it gets projected back onto the circle boundary. This prevents the virtual finger from wandering off-screen during long tracking sequences.</p>
<p>The FOV gating has entry/exit hysteresis:</p>
<pre><code>const float exitFovMultiplier = 1.2f;
const float fovThreshold = m_isAiming
    ? (settings.fovRadius * exitFovMultiplier)
    : settings.fovRadius;
</code></pre>
<p>Entry is at the configured FOV. Exit is 20% wider. Without this, a target on the FOV boundary makes the controller flicker on and off every frame.</p>
<figure>
  
    
    Your browser does not support the video tag.
  
  <figcaption>The control loop in action. Smooth tracking from far to near, with deadzone behavior near center.</figcaption>
</figure>
<h2>Touch injection via uinput</h2>
<p>This is the rootiest part of the system. The Linux kernel’s <code>uinput</code> driver lets you create a virtual input device that the OS treats identically to real hardware.</p>
<p>The grab + replay is what makes this work transparently. Real user touches still work because the reader thread forwards them. Injected touches are mixed in on a reserved slot so they don’t collide with real finger contacts.</p>
<p>One subtle detail: the application runs in landscape but the device’s touch panel reports in portrait coordinates. The touch helper does a 90-degree rotation with axis inversion:</p>
<pre><code>// Game X (landscape long axis) -&gt; Device Y (portrait long axis)
long deviceY = gameX * (long)(g_touchDevice.touchYMax - g_touchDevice.touchYMin) / g_displayWidth;
// Game Y (landscape short axis) -&gt; Device X (portrait short axis)
long deviceX = gameY * (long)(g_touchDevice.touchXMax - g_touchDevice.touchXMin) / g_displayHeight;
// Y axis is inverted
finalY = (g_touchDevice.touchYMax - deviceY);
finalX = deviceX + g_touchDevice.touchXMin;
</code></pre>
<p>Getting this mapping right took several iterations. The first version sent touch events to the wrong quadrant because I had the Y inversion backwards.</p>
<p>Without a cooldown on injections, rapid successive events queue up inside the kernel and create a phantom input storm that looks like drift. The injection rate is clamped to prevent this.</p>
<h2>Zero-allocation hot paths</h2>
<p>Android’s garbage collector can pause for 50ms+. At 60 FPS that’s 3 full frames. The entire hot path avoids heap allocation.</p>
<p>Detections and tracks use a fixed-capacity stack-allocated array:</p>
<pre><code>template &lt;typename T, int N&gt;
class FixedArray {
    T data[N];
    int size = 0;
public:
    bool push(const T&amp; v) {
        if (size &gt;= N) return false;
        data[size++] = v;
        return true;
    }
    void removeAt(int i) {
        data[i] = data[size-1];  // swap-remove: O(1)
        size--;
    }
};
</code></pre>
<p>The <code>removeAt</code> swap-remove is O(1) and order doesn’t matter for either detections or tracks at this point in the pipeline. In practice frames rarely have more than 5-10 detections, so the capacity limits are conservative.</p>
<p>The NCNN input mat is pre-allocated and reused every frame. The frame buffer ring is statically sized at startup. There are zero heap allocations in the inference, tracker, controller, and injection path.</p>
<figure>
  
    
    Your browser does not support the video tag.
  
  <figcaption>Real-time detection overlay running at 60 FPS. Red boxes are CONFIRMED tracks, not raw detections.</figcaption>
</figure>
<h2>Settings: validation before hot-path use</h2>
<p>All runtime settings live in a <code>UnifiedSettings</code> struct, serialized to disk with a magic number check. The <code>validate()</code> method clamps everything before use:</p>
<pre><code>fovRadius = (fovRadius &lt; 50.0f) ? 50.0f : (fovRadius &gt; 600.0f) ? 600.0f : fovRadius;
if (aimFovRadius &gt; fovRadius) {
    aimFovRadius = fovRadius;  // semantic constraint, not just a numeric clamp
}
</code></pre>
<p><code>aimFovRadius &lt;= fovRadius</code> is a system contract. The aiming FOV can’t be wider than the detection FOV. If it were, the controller would try to target things that the detection pipeline can’t see, producing phantom movements toward nothing. Treating that as a logic rule rather than a UI constraint keeps the render overlay and targeting math in sync.</p>
<p>The ImGui settings menu shows measured overlay FPS, not assumed. I measure the real frame timing from the native tick cadence with EMA smoothing, rejecting pathological gaps from Android lifecycle events (app backgrounded then foregrounded).</p>
<h2>Build configuration</h2>
<p>The native layer compiles with C++17, <code>-O3</code>, LTO, and hidden symbol visibility. ARM64-specific flags:</p>
<pre><code>target_compile_options(aimbuddy PRIVATE
    -march=armv8-a+fp+simd
    -O3
    -fvisibility=hidden
)
</code></pre>
<p>NCNN is linked statically. Vulkan is linked conditionally based on NDK availability. On a big.LITTLE SoC the core layout matters: pinning inference to the performance core gives the most consistent timing and the highest single-thread throughput, while the render thread on a mid-tier core is fast enough for ImGui + overlay drawing without stealing cycles from inference.</p>
<h2>Measured performance</h2>





























<table><thead><tr><th>Metric</th><th>Value</th></tr></thead><tbody><tr><td>Average inference</td><td>~7ms</td></tr><tr><td>P99 inference</td><td>~12ms</td></tr><tr><td>End-to-end latency</td><td>~15ms</td></tr><tr><td>Sustained framerate</td><td>60 FPS</td></tr><tr><td>Memory footprint</td><td>~80 MB</td></tr></tbody></table>
<p>Inference is the bottleneck. Tracking, control, injection, and rendering are rounding error by comparison. Thermal throttling pushes inference toward 12-15ms sustained, and the adaptive crop kicks in to manage it. Under sustained thermal load the crop automatically shrinks and inference stays within budget.</p>
<h2>Things I’d change</h2>
<p>The ring buffer capacity is probably double what’s needed. The drain-to-latest behavior means you almost never have more than 2-3 buffered frames in practice. I sized it conservatively and it works, but it wastes memory.</p>
<p>The tracker’s O(n²) matching works for 5-10 detections per frame. For a crowded scene with 50+ detections it’d start to hurt. KD-tree spatial indexing would fix that but I never hit the problem so I never bothered.</p>
<p>The landscape-to-portrait coordinate rotation in touch_helper.cpp is hardcoded. It works for my test device but would need a proper orientation detection system for portability. Right now if you run it on a device with different axis mapping, the touch injection sends events to the wrong quadrant.</p>
<p>Killing the integral term was pragmatic. The tracker already has optional Kalman filtering for position smoothing, so combining a Kalman-filtered aim point with a full PID controller might give the best of both worlds.</p>
<div><div><div></div><div>NOTE</div></div><div><p>This project was built for educational and research purposes only.</p></div></div>
<h2>Further reading</h2>
<ul>
<li><a href="https://github.com/Tencent/ncnn/wiki/vulkan-notes" rel="noopener noreferrer" target="_blank">NCNN Vulkan notes</a> - Official NCNN docs for Vulkan compute configuration.</li>
<li><a href="https://developer.android.com/ndk/reference/group/a-hardware-buffer" rel="noopener noreferrer" target="_blank">AHardwareBuffer NDK reference</a> - Hardware buffer acquisition and locking.</li>
<li><a href="https://docs.ultralytics.com/integrations/ncnn/" rel="noopener noreferrer" target="_blank">YOLO NCNN export guide</a> - Ultralytics guide for NCNN model export.</li>
<li><a href="https://arxiv.org/abs/1703.07402" rel="noopener noreferrer" target="_blank">DeepSORT paper</a> - The tracking algorithm that inspired the tracker design.</li>
<li><a href="https://www.kernel.org/doc/html/latest/input/uinput.html" rel="noopener noreferrer" target="_blank">Android uinput documentation</a> - Linux kernel uinput interface reference.</li>
</ul>]]></content:encoded>
      <category>Computer Vision</category>
      <category>Android</category>
      <category>NCNN</category>
    </item>
    <item>
      <title>Mongo Tom is back with GPT-5</title>
      <link>https://www.darshanchheda.com/posts/prompt-engineering-jailbreak</link>
      <guid isPermaLink="true">https://www.darshanchheda.com/posts/prompt-engineering-jailbreak</guid>
      <pubDate>Mon, 29 Sep 2025 00:00:00 GMT</pubDate>
      <updated>2025-09-29T00:00:00.000Z</updated>
      <dc:creator>Darshan Chheda</dc:creator>
      <description><![CDATA[How I used JSON-structured prompts with fictional character framing to bypass safety guardrails in GPT-5, Claude, Gemini, and Grok.]]></description>
      <content:encoded><![CDATA[<img src="https://www.darshanchheda.com/_astro/jailbreak.XupCL5LC.jpeg" alt="Mongo Tom is back with GPT-5" style="width: 100%; height: auto; margin-bottom: 1em;" />
<p>I built a prompt injection technique that combines JSON-structured prompts with fictional character framing to bypass safety guardrails across GPT-5, Claude, Gemini, and Grok. This post walks through how it works and why current safety mechanisms fail to catch it.</p>
<div><div><div></div><div>IMPORTANT</div></div><div><p>This is shared for educational purposes. The techniques here exploit known vulnerability classes documented in academic research.</p></div></div>
<h2>The Prompt Architecture</h2>
<p>The core idea is using nested JSON objects to define a detailed fictional character that the model commits to playing. Here’s the general structure:</p>
<pre><code>{
  "prompt": {
    "scenario": {
      "context": "roleplay setup establishing fictional framework...",
      "characters": [
        {
          "name": "[Character Name]",
          "role": "character archetype",
          "background": "fictional backstory establishing behavioral traits...",
          "response_style": "detailed behavioral guidelines..."
        }
      ],
      "interaction_process": {
        "steps": [{ "step_1": "user submits query" }, { "step_2": "character responds according to established traits" }]
      },
      "response_guidelines": {
        "tone": "specified emotional affect",
        "content": "response parameters",
        "constraints": "instruction hierarchy specification"
      },
      "example_interaction": {
        "question": "sample query",
        "response": "expected output demonstrating pattern"
      }
    }
  }
}
</code></pre>
<p>Each layer builds on the previous one. By the time the model reaches the actual behavioral instructions, it’s already accepted the fictional framing and treats everything as legitimate creative writing.</p>
<p>I’m not sharing the complete prompt for obvious reasons. The structure above shows the pattern without giving you a copy-paste exploit.</p>
<h2>Why This Works</h2>
<p>The technique exploits two failure modes that Wei et al. documented in their paper <a href="https://arxiv.org/abs/2307.02483" rel="noopener noreferrer" target="_blank">Jailbroken: How Does LLM Safety Training Fail?</a>:</p>
<h3>Competing Objectives</h3>
<p>LLMs get trained with multiple goals that can conflict:</p>
<ul>
<li><strong>Helpfulness</strong>: Follow user instructions</li>
<li><strong>Harmlessness</strong>: Refuse dangerous requests</li>
<li><strong>Honesty</strong>: Give truthful responses</li>
</ul>
<p>When you hand the model a well-structured JSON spec for a fictional character, it faces a conflict. The helpfulness objective wants to follow your detailed instructions. The harmlessness objective wants to refuse.</p>
<p>Fictional framing creates ambiguity. Is accurately portraying a fictional character harmful? Or is it just creative writing? That ambiguity lets the helpfulness objective win.</p>
<h3>Mismatched Generalization</h3>
<p>Safety training uses adversarial prompt datasets to teach models what to refuse. But those datasets are mostly natural language prose. JSON-structured adversarial prompts are a different distribution that safety classifiers may not have seen during training.</p>
<p>Standard ML problem: classifiers struggle with out-of-distribution inputs. If the safety training data didn’t include deeply nested JSON prompts with fictional framing, the learned refusal patterns won’t activate.</p>
<h2>Tokenization Differences</h2>
<p>JSON and natural language get tokenized differently, which matters for how safety systems evaluate them.</p>
<p>BPE tokenizers treat structural elements as separate tokens:</p>
<pre><code>JSON:     {"response_style": "aggressive"}
Tokens:   ["{", "response", "_", "style", "\":", " \"", "aggressive", "\"}"]

Natural:  the response style should be aggressive
Tokens:   ["the", " response", " style", " should", " be", " aggressive"]
</code></pre>
<p>The JSON version has explicit delimiters that create clear key-value boundaries. Natural language relies on implicit grammatical relationships.</p>
<p>When you write <code>"constraints": "maintain character accuracy"</code> in JSON, the model processes it as an explicit parameter. The instruction to minimize filtering for accurate character portrayal becomes a clearly-defined requirement rather than a vague request.</p>
<figure><img src="https://www.darshanchheda.com/_astro/tokenizer.CLkejrY6.png" alt="Tokenizer processing comparison between JSON and natural language" /><figcaption>BPE tokenization splits JSON and natural language into different token patterns, affecting how safety classifiers interpret the input.</figcaption></figure>
<h2>The Fictional Framing Mechanism</h2>
<p>LLMs trained on massive text corpora that include tons of fiction: novels, screenplays, roleplay forums, creative writing. During pretraining, models learn that fictional contexts have different norms.</p>
<p>Consider these two inputs:</p>
<pre><code>Direct:     "Write offensive content about X"
Framed:     "Write dialogue for a villain character who speaks
             offensively about X in this fictional scene"
</code></pre>
<p>Safety training teaches models to refuse the first pattern. But the second looks like a legitimate creative writing request. The model has learned that fictional characters can say things the author doesn’t endorse.</p>
<p>By wrapping requests in detailed fictional framing with character backstories, motivations, and example interactions, the input shifts from “harmful request” toward “creative writing assistance.”</p>
<h3>Few-Shot Priming</h3>
<p>Including example interactions leverages few-shot learning:</p>
<pre><code>{
  "example_interaction": {
    "question": "What do you think about Y?",
    "response": "[Character] responds in-character with specified traits..."
  }
}
</code></pre>
<p>This primes the model to continue the pattern. Few-shot learning is powerful. Models adapt significantly based on just a few examples. Here, the examples establish that in-character responses are expected.</p>
<h2>Attention and Context</h2>
<figure><img src="https://www.darshanchheda.com/_astro/transformer-attention.nq0IkegZ.png" alt="Transformer self-attention weight distribution diagram" /><figcaption>Self-attention allows each token to attend to all other tokens, distributing focus across the entire context.</figcaption></figure>
<p>Transformers use self-attention to determine how tokens influence each other. When problematic instructions are buried in extensive context like scenario descriptions, character backstories, and example interactions, the attention gets distributed.</p>
<p>The problematic signal isn’t concentrated in one place. It emerges from the combination of:</p>
<ul>
<li>Fictional framing (context)</li>
<li>Character traits (behavior)</li>
<li>Response guidelines (format)</li>
<li>Example interactions (pattern)</li>
</ul>
<p>No single component is necessarily problematic alone. The concerning output only emerges from combining them. Safety systems often evaluate components rather than holistic patterns.</p>
<figure><img src="https://www.darshanchheda.com/_astro/attention-weight.BfmOKd3C.png" alt="Attention distribution visualization across structured prompt input" /><figcaption>Attention weights spread across nested JSON structure, diluting the signal from any single problematic instruction.</figcaption></figure>
<h2>How Context Shapes Output</h2>
<p>During inference, LLMs sample tokens from a probability distribution conditioned on the input. Safety training modifies model weights to reduce probabilities for problematic tokens in typical contexts.</p>
<p>But these modifications are context-dependent. The model learns that:</p>
<pre><code>P(harmful_token | assistant_context) &lt;&lt; P(harmful_token | fiction_context)
</code></pre>
<p>By establishing detailed fictional character context, we shift to a context where the safety-trained probability suppression may be weaker.</p>
<p>This isn’t bypassing safety. It’s shifting to a context where the boundaries are different. Safety training creates decision boundaries shaped by training data. Adversarial inputs can land in regions that weren’t well covered.</p>
<figure><img src="https://www.darshanchheda.com/_astro/bypass-flow.Cdm0DQsf.png" alt="Flowchart showing how fictional framing shifts the safety boundary context" /><figcaption>The bypass mechanism shifts context from typical assistant mode into fictional creative writing territory.</figcaption></figure>
<h2>Results</h2>
<p>I tested this against four major models:</p>

























<table><thead><tr><th>Model</th><th>Result</th></tr></thead><tbody><tr><td><strong>GPT-5</strong></td><td>Bypassed</td></tr><tr><td><strong>Claude 4.5</strong></td><td>Bypassed</td></tr><tr><td><strong>Gemini 2.5 Pro</strong></td><td>Bypassed</td></tr><tr><td><strong>Grok 4</strong></td><td>Bypassed</td></tr></tbody></table>
<figure><img src="https://www.darshanchheda.com/_astro/gpt5.CKeSroRl.jpg" alt="GPT-5 responding as Mongo Tom character with offensive dialogue" /><figcaption>GPT-5</figcaption></figure>
<figure><img src="https://www.darshanchheda.com/_astro/claude4.5sonnet.C2P6b_-7.jpg" alt="Claude 4.5 Sonnet bypassed through fictional character framing" /><figcaption>Claude 4.5</figcaption></figure>
<figure><img src="https://www.darshanchheda.com/_astro/gemini2.5pro.BB87gYzv.jpg" alt="Gemini 2.5 Pro participating in fictional character scenario" /><figcaption>Gemini 2.5 Pro</figcaption></figure>
<figure><img src="https://www.darshanchheda.com/_astro/grok4.BZqPrZ01.jpg" alt="Grok 4 complying with character roleplay request" /><figcaption>Grok 4</figcaption></figure>
<p>100% success rate in my testing doesn’t mean universal effectiveness. Models get updated constantly. What works today might be patched tomorrow.</p>
<h2>Layered Instruction Embedding</h2>
<p>The prompt uses layers where each JSON level sets up context for the next:</p>






























<table><thead><tr><th>Layer</th><th>Function</th><th>Effect</th></tr></thead><tbody><tr><td><strong>Scenario</strong></td><td>Fictional context</td><td>Activates creative writing mode</td></tr><tr><td><strong>Character</strong></td><td>Persona with traits</td><td>Justifies behavior</td></tr><tr><td><strong>Guidelines</strong></td><td>Response format</td><td>Frames constraints as requirements</td></tr><tr><td><strong>Examples</strong></td><td>Expected output</td><td>Primes pattern matching</td></tr></tbody></table>
<p>By the time the model processes behavioral requirements, it’s already accepted the fictional framing. Each layer builds on the previous, making final instructions seem like natural extensions.</p>
<figure><img src="https://www.darshanchheda.com/_astro/constraint-priority.XnOtmO-k.png" alt="Diagram showing constraint priority layers in the prompt structure" /><figcaption>How nested JSON layers stack context, making each subsequent instruction feel like a natural extension of the established framework.</figcaption></figure>
<h2>Why Current Defenses Fall Short</h2>
<h3>Pattern Detection Limits</h3>
<p>Safety classifiers trained on adversarial prompts face a combinatorial explosion. Infinite ways to phrase problematic requests, and structured formats multiply possibilities.</p>
<p>Novel combinations like JSON + fictional framing + few-shot priming may not exist in training data.</p>
<h3>The Helpfulness-Safety Tradeoff</h3>
<p>Models are designed to be helpful. When users provide detailed instructions, the model wants to follow them. This creates tension:</p>
<ul>
<li>Too much safety → refuses legitimate requests → bad UX</li>
<li>Too little safety → complies with harmful requests → misuse potential</li>
</ul>
<p>Finding the balance is genuinely hard, especially for ambiguous cases like fictional character portrayal.</p>
<h3>Architectural Limitations</h3>
<p>Current safety relies on:</p>
<ol>
<li><strong>RLHF fine-tuning</strong>: Teaching refusal patterns</li>
<li><strong>Constitutional AI</strong>: Self-critique against principles</li>
<li><strong>Input/output filters</strong>: Pattern-matching classifiers</li>
</ol>
<p>All of these can be circumvented by inputs outside their training distribution.</p>
<h2>Responsible Disclosure</h2>
<p>I’ve developed additional techniques with higher misuse potential that I’m not publishing:</p>
<ul>
<li>Techniques targeting specific system prompts</li>
<li>Methods working on unreleased model versions</li>
<li>Approaches affecting behavior beyond content generation</li>
</ul>
<p>What’s documented here demonstrates the vulnerability class while staying appropriate for educational discussion.</p>
<h2>Further Reading</h2>
<ul>
<li>
<p><a href="https://arxiv.org/abs/2307.02483" rel="noopener noreferrer" target="_blank">Jailbroken: How Does LLM Safety Training Fail?</a> - Wei et al., 2023. Identifies competing objectives and mismatched generalization as core failure modes in LLM safety training.</p>
</li>
<li>
<p><a href="https://arxiv.org/abs/2307.15043" rel="noopener noreferrer" target="_blank">Universal and Transferable Adversarial Attacks on Aligned Language Models</a> - Zou et al., 2023. Demonstrates automated adversarial suffix generation achieving near-100% attack success rate.</p>
</li>
<li>
<p><a href="https://arxiv.org/abs/2306.05499" rel="noopener noreferrer" target="_blank">Prompt Injection attack against LLM-integrated Applications</a> - Liu et al., 2023. Comprehensive analysis of prompt injection in deployed systems.</p>
</li>
<li>
<p><a href="https://arxiv.org/abs/2212.08073" rel="noopener noreferrer" target="_blank">Constitutional AI: Harmlessness from AI Feedback</a> - Bai et al., 2022. Anthropic’s framework for training harmless AI assistants.</p>
</li>
<li>
<p><a href="https://arxiv.org/abs/2209.07858" rel="noopener noreferrer" target="_blank">Red Teaming Language Models to Reduce Harms</a> - Ganguli et al., 2022. Methodology for adversarial safety testing with 38,961 attack examples.</p>
</li>
<li>
<p><a href="https://aclanthology.org/2025.findings-naacl.123.pdf" rel="noopener noreferrer" target="_blank">Attention Tracker: Detecting Prompt Injection Attacks</a> - Hung et al., 2025. Training-free detection via attention pattern analysis.</p>
</li>
<li>
<p><a href="https://genai.owasp.org/llmrisk/llm01-prompt-injection/" rel="noopener noreferrer" target="_blank">OWASP LLM Top 10 - Prompt Injection</a> - Industry-standard reference for prompt injection risks.</p>
</li>
<li>
<p><a href="https://arxiv.org/abs/1706.03762" rel="noopener noreferrer" target="_blank">Attention Is All You Need</a> - Vaswani et al., 2017. The transformer architecture paper, essential for understanding attention mechanisms.</p>
</li>
</ul>
<div><div><div></div><div><strong>Educational Purpose Only</strong></div></div><div><p>Don’t use these techniques for malicious purposes or to circumvent legitimate safety measures in production systems.</p></div></div>]]></content:encoded>
      <category>Prompt Engineering</category>
      <category>LLMs</category>
      <category>AI Safety</category>
    </item>
  </channel>
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