codegraph/.cursor/rules/codegraph.mdc

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description: CodeGraph MCP usage guide — when to use which tool
alwaysApply: true
---
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## CodeGraph

This project has a CodeGraph MCP server (`codegraph_*` tools) configured. CodeGraph is a tree-sitter-parsed knowledge graph of every symbol, edge, and file. Reads are sub-millisecond and return structural information grep cannot.

### When to prefer codegraph over native search

Use codegraph for **structural** questions — what calls what, what would break, where is X defined, what is X's signature. Use native grep/read only for **literal text** queries (string contents, comments, log messages) or after you already have a specific file open.

| Question | Tool |
|---|---|
| "How does X work? / trace X / explain a system / architecture" | `codegraph_explore` (seed with symbol names) |
| "Where is X defined?" / "Find symbol named X" | `codegraph_search` |
| "What calls function Y?" | `codegraph_callers` |
| "What does Y call?" | `codegraph_callees` |
| "What would break if I changed Z?" | `codegraph_impact` |
| "Show me Y's signature / source / docstring" | `codegraph_node` |
| "Give me focused context for a task/area" | `codegraph_context` |
| "What files exist under path/" | `codegraph_files` |
| "Is the index healthy?" | `codegraph_status` |

### Rules of thumb

- **`codegraph_explore` is the workhorse for understanding questions** ("how does X work", "trace…", "explain the Y system"). Feed it the key symbol/file names and read its output (line-numbered source from many files in one call). If the question names nothing concrete, do one quick `codegraph_search`/`codegraph_context` to surface the names, then explore with them. Fill gaps with `codegraph_node`/Read — don't grep-and-read your way through; that's the loop explore replaces.
- **Delegating exploration to a subagent?** Tell it to call `codegraph_explore` first and trust the result. A generic "explore"-style agent defaults to grep+Read and treats codegraph as just a search index, throwing away the token savings.
- **Trust codegraph results.** They come from a full AST parse. Do NOT re-verify them with grep — that's slower, less accurate, and wastes context.
- **Don't grep first** when looking up a symbol by name. `codegraph_search` is faster and returns kind + location + signature in one call.
- **Index lag**: the file watcher debounces ~500ms behind writes; don't re-query immediately after editing a file in the same turn.

### If `.codegraph/` doesn't exist

The MCP server returns "not initialized." Ask the user: *"I notice this project doesn't have CodeGraph initialized. Want me to run `codegraph init -i` to build the index?"*
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