Mutmut MCP

A Model Context Protocol (MCP) server for managing mutation testing with mutmut. This tool provides a set of programmatic APIs for running mutation tests, analyzing results, and improving test coverage in Python projects.

Features

• Run mutation testing sessions on any Python module or package

• Show overall mutation testing results and surviving mutations

• Suggest areas needing better test coverage

• Rerun mutmut on specific survivors or all survivors

• Clean mutmut cache

• Designed for automation and integration with other MCP tools

Related MCP server: MCP Python Server

Install

# Run directly from GitHub (no install needed)
uvx --from git+https://github.com/wdm0006/mutmut-mcp mutmut-mcp

# Or install from source
git clone https://github.com/wdm0006/mutmut-mcp
cd mutmut-mcp
uv sync
uv run mutmut_mcp.py

Installing via Smithery

To install mutmut-mcp for Claude Desktop automatically via Smithery:

npx -y @smithery/cli install @wdm0006/mutmut-mcp --client claude

MCP Client Configuration

{
  "mcpServers": {
    "mutmut": {
      "command": "uvx",
      "args": ["--from", "git+https://github.com/wdm0006/mutmut-mcp", "mutmut-mcp"]
    }
  }
}

API / Tools

The following tools are available:

• run_mutmut(target, options="", venv_path=None, project_path=None) – Run a mutation testing session on the target

• show_results(venv_path=None, project_path=None) – Show overall results

• show_survivors(venv_path=None, project_path=None) – List surviving mutations, plus a labelled section for mutants no test covers

• rerun_mutmut_on_survivor(mutation_id=None, venv_path=None, project_path=None) – Rerun mutmut on a specific survivor or all survivors

• clean_mutmut_cache(venv_path=None, project_path=None) – Clean mutmut cache

• show_mutant(mutation_id, venv_path=None, project_path=None) – Show the code diff and details for a specific mutant

• prioritize_survivors(venv_path=None, project_path=None) – Rank uncovered mutants and survivors by likely materiality

project_path

Every tool accepts an optional project_path: the directory containing the project's mutmut configuration ([mutmut] paths_to_mutate= in setup.cfg / pyproject.toml), its source, its tests, and mutmut's mutants/ state directory. Mutmut runs with that directory as its working directory, and clean_mutmut_cache removes state only from inside it.

Pass it whenever the server was not launched from the project directory — which is typical for desktop MCP clients and uvx. Omitted, the tools fall back to the server process's working directory, so existing calls behave as before. A project_path that is not an existing directory returns an error without running mutmut or deleting anything.

venv_path

venv_path points at the virtual environment holding the project's mutmut (the tools use <venv>/bin/mutmut, or <venv>\Scripts\mutmut.exe on Windows); omitted, mutmut is taken from PATH. A relative venv_path is resolved against project_path when both are given, so the common .venv form works:

{ "project_path": "/home/me/src/myproject", "venv_path": ".venv" }

License

This project is licensed under the MIT License. See LICENSE for details.