# Mutate

> Use as a thin compatibility skill when the user asks for the old mutate command; delegate to atdd-mutate for mutation testing and differential mutation workflow.

- Skill: `kdoronin/mutate` (Agent Skill)
- Install (CLI): `npx skillmds@latest add kdoronin/mutate`
- Raw SKILL.md: https://api.skillmd.com/api/skills/kdoronin/mutate/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Productivity
- Author: kdoronin (https://skillmd.com/u/kdoronin)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/kdoronin/mutate

---


Run mutation testing on this project by following the `atdd-mutate` skill. This
skill exists as a Codex-native compatibility wrapper for the legacy mutate
entrypoint.

## Instructions

1. Check that both test streams are green before proceeding:
   - Run the unit tests
   - Run acceptance tests if a pipeline exists (`./run-acceptance-tests.sh`)
   - If either fails, report the failure and stop — do not mutate against a red baseline

2. Detect the project language and check if a mutation tool exists in the project.
   - **Preferred:** Build a custom mutation tool using TDD — a project-specific
     module that walks the AST, applies mutations one at a time, runs targeted
     tests, and reports survivors. See the `atdd-mutate` skill for the 4-module
     architecture (mutations, runner, core, hashing/selection) and mutation
     categories.
   - **Alternative:** If the user requests a faster setup, install an existing
     framework (Stryker, mutmut, PIT, etc. — see the `atdd-mutate` skill).

3. Configure the tool to:
   - Target source code only (not tests, specs, generated files, or pipeline code)
   - Exclude `generated-acceptance-tests/`, `acceptance-pipeline/`, and `specs/`
   - If `$ARGUMENTS` is provided, scope mutations to that path

4. Run the mutation tool. On the custom-tool path, run `dae_mutmap.py select`
   first and mutate only the changed functions it returns (differential
   mutation testing — see the `atdd-mutate` skill); on the framework path,
   enable the framework's incremental flag.

5. Report results:
   - Mutation score (percentage)
   - Total mutants, killed, survived
   - List each surviving mutant with: file, line, mutation description
   - Assessment: strong (90%+), moderate (70-89%), or weak (<70%)
   - On the custom-tool path, run `dae_mutmap.py update` to refresh
     `mutation-manifest.json`; combine fresh results with cached entries for
     unchanged functions

6. Ask whether to proceed with killing surviving mutants by using the
   `kill-mutants` skill.