myelixlabs/synapse-mcp

**A persistent code-knowledge graph for AI agents. Runs locally. Writes safely.**
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> 🏗️ **Currently in Preview.** Synapse MCP is actively evolving. We want your feedback — open an issue to tell us what breaks, what's missing, or what would make you switch from grep for good.
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Synapse MCP is a **free, 100% local MCP server** that turns your codebase into a persistent, in-memory AST knowledge graph. Claude, Cursor, Copilot, and every MCP-compatible agent gets exact caller trees, semantic search, safe atomic writes, and diff-aware change review — without a single byte of your code leaving the machine.
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What Synapse actually does
Most code-graph tools stop at discovery: index the codebase, answer questions about it, done. Synapse goes further.
It runs as a **persistent BEAM daemon** — not a CLI you invoke, but a long-lived process that keeps your graph in memory across sessions. It watches files for changes automatically (inotify / FSEvents / kqueue) and re-indexes only the changed files, not the whole workspace. When you pull new commits it detects the new Git HEAD and re-indexes only the diff.
On top of that it adds what no competitor offers: **safe write capability**. Before any proposed edit touches disk, Synapse simulates it in memory, validates it against the compiler and linter, maps the blast radius, and only commits atomically on passing every gate. If anything fails it rolls back. Your files are never left broken.
In plain terms
Think of the difference between a new employee on their first day versus a senior engineer who has worked in the codebase for years.
The new employee opens files, searches for things, asks questions, gets confused by unfamiliar names. Every task starts with exploration.
The senior engineer already knows where everything is. They go straight to the right file, understand the downstream effects of a change before touching it, and know which tests to run. They don't explore — they act.
**Synapse turns your AI agent into the senior engineer.** The knowledge graph is built once, updated automatically as your code changes, and queried instantly on every agent request — all without any code leaving your machine.
Why should I use it?
| Without Synapse | With Synapse |
|---|---|
| Agent greps files, reads imports, opens 10 files to find one function | One tool call returns the exact chunk, its callers, and its tests |
| Every session starts from zero | Graph persists and improves across sessions |
| Agent writes a file, lint fails, file is broken | write_safely validates first, rolls back on failure |
| You paste a stack trace and hope | resolve_stack maps it directly to your AST and suggests a fix |
| Code review is manual | review_diff ranks blast radius and broken contracts before you push |
| Code sent to a cloud service to build an index | Everything runs locally — zero data egress |
You don't change how your agent works. You don't change your workflow. You install Synapse, register your repo, and your agent gets smarter immediately.
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What your agent gets
| Tool group | What it does |
|---|---|
| ask_synapse | Natural-language entry point — routes to the right tool automatically |
| synapse_get_context | Pre-built structural slices: callers, callees, contracts, summaries |
| synapse_search_codebase | Semantic (BM25F + embeddings), symbol, and regex — structured chunk IDs, not file dumps |
| synapse_explore_graph | Transitive caller / callee traversal, cycle detection, context |
| synapse_modify_files | Simulate → validate → write atomically → rollback on lint failure |
| synapse_change_review | Diff analysis, blast-radius ranking, broken-contract detection |
| synapse_debug_trace | Stack trace → AST root cause → reproducing test suggestions |
| synapse_test_quality | Coverage bands, test mapping, ranked gap targets |
| synapse_codebase_insights | Dead-code deletion safety, public API surface, dependency graph, refactor opportunities |
| synapse_knowledge_cache | Persistent summaries and retrieval reinforcement across sessions |
| synapse_manage_repos | Multi-repo registry — register, archive, restore; Git worktree support |
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Benchmark — Autonomous Security Audit · 500k LOC · Same Frontier Model