Codebase Cartographer

An MCP server that maps a local Python repository into an AST-backed symbol graph and performs verified multi-file refactors on it.

Most coding agents refactor by grepping for a string and rewriting what they find. That approach cannot tell a call to compute() apart from a local variable that happens to be named compute, and it has no idea which twelve files break when you rename it. This server gives the model a real index instead: scope-resolved references, an import graph, and a two-phase edit protocol that refuses to write anything it cannot verify.

What it does

Maps. Walks the repository (honouring .gitignore), parses every module, and builds a symbol table of functions, classes, methods, and module-level variables, plus the import graph between modules.

Resolves. Finds references using real scope analysis — the LEGB chain, global and nonlocal declarations, comprehension scopes, walrus bindings, and the rule that class bodies are invisible to nested functions. A local variable that shadows a module-level symbol is not a reference to it, and the tool knows the difference.

Refactors. Renames, moves, and deletes symbols across every file that touches them — rewriting from x import y, import x + x.y attribute access, as aliases, and __all__ entries. Nothing is written until you apply a plan you have seen the diff for.

Related MCP server: MCP Python Code Navigation Server

Safety model

Refactoring is two-phase, and the first phase never touches disk.

1. plan_rename_symbol / plan_move_symbol / plan_delete_symbol return a plan id, a unified diff, and a list of warnings. Every touched file's content hash is recorded.

2. apply_plan re-checks those hashes (aborting if anything changed on disk since planning), builds the new content for every file, re-parses each one, and refuses to write if any file would end up unparseable. Originals are copied to .cartographer-backups/<plan_id>/. A failure mid-write rolls every file back.

Further guardrails: paths outside the mapped root are rejected; renaming a method requires an explicit allow_heuristic=true because attribute matching cannot be resolved without type inference; deleting a symbol that still has references is refused unless forced.

What it cannot see

Static analysis has a hard edge, and the tool is built to say where that edge is rather than to pretend it isn't there.

find_dynamic_references reports string literals matching a symbol name — getattr(mod, "compute"), plugin registries, dotted settings strings, entry-point tables — and detects imports of underscore-prefixed native modules. Those warnings are attached to every refactor plan.

This matters concretely. Renaming JSONDecodeError in a copy of the stdlib json package rewrites all 19 Python references correctly and still breaks the package, because the _json C accelerator resolves that name at runtime through the C API. No pure-Python analysis can follow that. The tool flags the native accelerator import and tells you to check by hand.

Also invisible: from x import * re-exports (reported as a warning), runtime monkey-patching, and references from other languages or config files.

Tools

Install

pip install -e .

Register it with an MCP client:

{
  "mcpServers": {
    "codebase-cartographer": {
      "command": "python",
      "args": ["-m", "cartographer"],
      "env": { "CARTOGRAPHER_ROOT": "/path/to/your/repo" }
    }
  }
}

CARTOGRAPHER_ROOT is only the default for map_repository; the tool takes an explicit root argument too.

A typical session

map_repository(root="~/work/service")
  -> 412 files, 1 import cycle, 38k LOC

impact_of_change(module="service.auth.tokens")
  -> 23 transitive dependents

find_references(qualname="service.auth.tokens.decode_jwt")
  -> 31 references across 12 files

find_dynamic_references(name="decode_jwt")
  -> 1 string literal in service/registry.py:44   <- read this before proceeding

plan_rename_symbol(qualname="service.auth.tokens.decode_jwt", new_name="decode_access_token")
  -> plan 9f2a1c: 31 edits across 12 files, with diff

apply_plan(plan_id="9f2a1c")
  -> written, backed up to .cartographer-backups/9f2a1c/

Development

pip install -e ".[dev]"
pytest

65 tests cover scope resolution (shadowing, global, comprehensions, class-body visibility), reference finding across every import style, rename/move/delete correctness, generated-import style, and the apply-phase guarantees: stale-file detection, syntax validation, and rollback.

The suite's strongest check is that the tool refactors its own source — renaming a function across the implementation and the tests, and moving one between modules — after which the full suite still passes against the rewritten copy.

Requirements

Python 3.10+ (uses ast.alias position attributes). Python source only.

License

MIT