| name | codegraph |
| description | Pre-indexed code knowledge graph (MCP, SQLite + tree-sitter) for faster, lower-token exploration of brownfield codebases. Use when starting work on a repo larger than ~500 files or when the task involves cross-file traversal — "where is X used", "what calls Y", "what breaks if I change Z", "trace flow from A to B", "explain this subsystem". Skip for single-file edits or sessions shorter than the cold-start cost. Triggers include "codegraph", "code graph", "index this repo", "where is X defined", "find callers of", "callees of", "blast radius of changing X", "explore this codebase". Cuts the grep + Read loops needed to orient, via O(1) SQLite lookups and FTS5 search over 8 MCP tools — but it's an unsound tree-sitter approximation, so grep stays the completeness backstop for renames/exhaustive callers. |
codegraph
Local code graph exposed as 8 MCP tools. Accelerates exploration with O(1) SQLite lookups and FTS5 search — slashing the grep + Read loops needed to orient in a codebase.
It does not replace grep. Codegraph is a tree-sitter approximation of the call graph, not a compiler-grade one: it is fast and low-token but unsound (it has false negatives). Treat it as the accelerator for orientation and traversal, and keep grep as the source of truth for completeness. See Soundness & limits below — this distinction is load-bearing, not a footnote.
When to use
- Brownfield repo where structure is non-obvious
- Task involves: "where is X used", "what breaks if I change Y", "trace flow from A to B"
- Long-running session — cold-start cost amortizes over multiple queries
When NOT to use
- Single-file edits or trivial lookups
- Session likely shorter than cold-start cost (see
references/spike.md for per-repo numbers)
- Repo not initialized AND no cached
.codegraph/ AND short session
Soundness & limits — read before trusting a result
Codegraph is built on tree-sitter, not the compiler, so its call/reference edges are an approximation. It fails in three confirmed ways. The governing rule falls out of them:
Grep is the source of truth for completeness. Codegraph is the accelerator for orientation and traversal. Never invert these.
The asymmetry is the whole argument: for a refactor, a false negative is dangerous (you miss a caller, ship a break); a false positive is merely annoying (you glance and discard). Codegraph has false negatives; grep does not. So codegraph may propose and rank, but grep confirms whenever the answer must be exhaustive.
The three failure modes (measured on a ~580-file Rust+TS repo):
- Unsound edges → false negatives.
callers/callees/impact miss real call sites when the receiver type can't be resolved from syntax alone (calls on locals, generics, trait objects). Measured: a method with 8 real callers returned 2 — the 5 dropped were local.method() and generic-dispatch sites, with no warning. Exact on unique free-functions + direct calls (verified 1/1, 2/2); unreliable on method dispatch.
- Name resolution is fuzzy and overload-blind. Bare-name queries prefix-match (
useWorkspace answered for useWorkspacesQuery — a different symbol) and conflate overloads (execute, with 19 definitions, returned sqlx's .execute() DB calls, not the trait method). For any name with multiple definitions, drop to codegraph_node on a specific symbol id; bare callers/callees are unattributable.
- The index lags the disk. CLI sees nothing until
codegraph sync (~0.3s); the MCP file-watcher closes the gap to ~1–2s. Right after an edit, the index is wrong — grep/Read is ground truth until it catches up.
Decision matrix
| Task | Tool | Why |
|---|
| Orient / "explain subsystem X" / first survey | codegraph explore | One call, ranked, verbatim source — far less context than grep+Read |
| Callers of a uniquely-named free function | codegraph callers (trust it) | Exact on unique names + direct calls |
| Find ALL callers before a signature change / rename | grep authoritative; codegraph only to pre-rank | Codegraph is unsound here — completeness can't depend on it |
Anything with an overloaded name (execute, lookup, run, new) | grep, or codegraph node on a specific id | Bare-name codegraph conflates / under-resolves unpredictably |
| Impact of a core type | codegraph impact --depth 1 to pre-rank, then grep to confirm | Default depth-2 inflates (test fns + one file entry per file) and isn't depth-ranked |
| Just-edited code | grep (or codegraph sync first) | Index is stale until reindex |
| Trait-dispatch / generic call sites | grep + reading | Both weak; codegraph silently drops them, grep at least surfaces the text |
Workflow: start with explore for the map and callers/impact for direction — but the moment the answer must be complete (a rename, "did I get everyone?"), confirm with grep and treat any codegraph-vs-grep delta as "codegraph missed it," not "grep over-matched."
Prerequisites
- Node 18+ on PATH
- Project has
.codegraph/ (run codegraph init if not)
- For cloud sessions: cold-start cost verified via
references/spike.md for the target repo
Files
references/install.md — installation for local / Claude Code Cloud / devcontainerreferences/usage.md — which of the 8 MCP tools to use when, with main-session vs subagent rulesreferences/spike.md — cold-start measurement protocol; run once per new target repo before relying on codegraph in cloud sessions
Known integration targets
Cold-start measured locally (Node 22, 4 cores). Cloud cold-start still pending — re-run references/spike.md in a cloud session before relying on these numbers there.
| Repo | Indexed files | Nodes / edges | DB size | Cold init+index | Query wall |
|---|
| onsager-ai/onsager | 578 (rust + tsx/ts) | 8.6k / 20k | 24 MB | 12s | ~0.9s |
| crawlab-team/crawlab | 644 (go) | 6.8k / 15k | 11 MB | 6s | ~0.9s |
| codervisor/leanspec | 695 (tsx/rust/ts) | 8.9k / 21k | 23 MB | 10s | ~0.9s |
Per-query wall is dominated by Node startup — the SQLite work itself is milliseconds. End-to-end cold-start including one-shot npx install is ~13–19s for repos in this size class.
