diffctx MCP server

diffctx — what a git change reaches, and the code to review it

diffctx tells an agent or a reviewer what a change reaches outside its diff — the callers, the tests that reach them, the contracts it crosses — and selects the code needed to understand it under a token budget. Local, deterministic, no index, no model calls. Caller resolution is static and per language; where it cannot resolve, the answer says so instead of printing a zero.

Formerly published as treemapper — every command, flag, and API call works unchanged.

Install

diffctx is a command-line tool; the MCP server, the Claude Code plugin and the GitHub Action run the same engine.

CLI

uvx diffctx . --diff HEAD~1             # zero-install, run once via uv
pipx install diffctx                    # isolated CLI
pip install diffctx                     # into an active environment
cargo install diffctx                   # native binary from crates.io, no Python
npx diffctx . --diff HEAD~1             # npm wrapper over the native binary
docker run --rm -v "$PWD:/repo" ghcr.io/nikolay-e/diffctx . --diff HEAD~1

scoop bucket add diffctx https://github.com/nikolay-e/diffctx   # Windows
scoop install diffctx/diffctx

The native binary — cargo, npm, Docker, Scoop and the release archives for Linux, macOS and Windows on x64 and ARM — answers --diff and --symbol in every mode; whole-tree export, Markdown packs, diffctx graph and the MCP server need the Python package.

Any MCP client

Registered as io.github.nikolay-e/diffctx.

claude mcp add diffctx -- uvx --from 'diffctx[mcp]' diffctx-mcp
codex mcp add diffctx -- uvx --from 'diffctx[mcp]' diffctx-mcp
gemini mcp add diffctx uvx -- --from 'diffctx[mcp]' diffctx-mcp

Cursor, VS Code, Claude Desktop, Windsurf, Zed, Continue and the Python API: integrations.

Claude Code plugin

The MCP server plus /diffctx:impact and hooks that run it on each commit and push.

claude plugin marketplace add nikolay-e/diffctx
claude plugin install diffctx@diffctx

CI

The GitHub Action hands a pull request's diff context to any review step.

Usage

diffctx . --diff --mode impact          # uncommitted work: callers outside the diff, their tests, contracts
diffctx . --symbol parse_config         # the same for a name, no change needed
diffctx . --diff main...feature         # the code to review a branch, packed under the auto budget
diffctx . --diff HEAD~1 --budget 12000  # the last commit, capped at 12k o200k tokens
diffctx . --diff 24h --mode locate      # today's work as ranked JSON, no source bodies
diffctx .                               # whole-tree export, Markdown

--diff takes a git range, staged, or a duration window ending now (24h, 90min, 2w). Every flag, default and exit code: command-line reference.

How it compares

Whole-repo packers export everything; code-graph servers answer queries against a maintained index. diffctx is diff-seeded: the input is a change, the output is what it touches and what explains it. Measured results, and when the other two fit better: COMPARISON.md.

More

• Documentation site — the pipeline end to end
• Command-line reference — rendered from diffctx --help
• Integrations — install, MCP clients, Python API
• FAQ — heuristic or oracle, ignore rules, monorepos, secrets
• Token counting — --budget for non-GPT models
• Benchmarks and the paper
• Changelog · Security
• Parameter strategy

Apache 2.0