llms.txt@docs · diff

git:20261024.18ef483 to git:20261026.80198df

9 added, 2 removed. Audit A to A.

# Mutineer

> Mutineer checks whether your Ruby tests would catch a bug. It makes one small

> code change at a time and runs your Minitest or RSpec tests. Each changed version

> is a mutant. A failing test kills it; passing tests let it survive. Review each

> survivor for a missing test or a change that leaves the behaviour unchanged.

Line coverage shows which lines ran. Mutation testing checks whether the tests

notice a change. Start with one file and understand the results before adding a CI gate.

Key facts:

- - **Written from scratch**: no code from Mutant or any other mutation-testing tool. MIT for every use. How it differs from Mutant: [README](https://github.com/davidteren/mutineer#mutineer-and-mutant).

+ - **Written from scratch**: no code from Mutant or any other mutation-testing tool. MIT for every use. How it differs from Mutant: [comparison guide](https://github.com/davidteren/mutineer/blob/main/docs/comparison.md#mutineer-and-mutant).

- **Zero runtime dependencies** — Prism + stdlib only. No `eval`. Test-framework changes stay in disposable child processes.

- **One mutation per mutant**, validity-checked by re-parsing; 21 mutation operators.

- **Fork-isolated, parallel** execution (Linux + macOS); coverage-guided per-line test selection.

- **Programmatic**: versioned JSON contract, structured exit codes (0 pass / 1 below threshold, incomplete run, baseline regression or runtime error / 2 misinvocation), `--since` diff-scoped runs, `--threshold` hard gate, `--baseline` delta gating.

- **Rails**: Minitest `--daemon` boots the app once and forks per mutant with per-worker DB isolation (SQLite file, PostgreSQL, or MySQL 8 test databases) so `--jobs N` is parallel-safe.

- **Production readiness**: [Is it production-ready?](https://github.com/davidteren/mutineer#is-it-production-ready) has the support matrix. The docs home page shows the same section.

- Distributed as a RubyGem and a GitHub Action (composite `action.yml`).

## Docs

- [Overview, operators, and usage](https://davidteren.github.io/mutineer/): what Mutineer is, the mutation operators, install, and CLI flags.

- [Mutation testing, explained](https://davidteren.github.io/mutineer/learn.html): a runnable first example, report terms, and what to do with a survivor.

- [For AI agents & CI](https://davidteren.github.io/mutineer/agentic-coding.html): the agent inner loop, CI regression gating, the GitHub Action, and equivalent-mutant suppression.

- [Equivalent skips](https://davidteren.github.io/mutineer/equivalent-skips.html): code changes Mutineer skips automatically, and why.

- [Rails rollout](https://davidteren.github.io/mutineer/rails.html): four stages from one Rails model to a CI gate, plus GitHub Actions and GitLab CI recipes.

+ - [Quick start](https://davidteren.github.io/mutineer/quick-start.md): install, a first run on one file, and one fixed survivor, with agent prompts.

+ - [First run to steady state](https://davidteren.github.io/mutineer/getting-started.md): from one file to a baseline and a CI check on changed code, with agent prompts.

+ - [Reading results](https://davidteren.github.io/mutineer/results.md): report rows, fixing survivors, suppressing equivalent mutants, mutant ids, and the kill matrix.

+ - [Rails setup](https://davidteren.github.io/mutineer/rails-setup.md): `--rails`, the `--daemon` backend, worker databases, Spring and Bootsnap, and apps on Ruby < 3.4.

+ - [CI: changed code and baselines](https://davidteren.github.io/mutineer/ci.md): `--since`, `--baseline`, the GitHub Action and its inputs, baseline refresh, and timeouts.

+ - [CLI reference](https://davidteren.github.io/mutineer/cli.md): every `mutineer run` flag with its default, and the `.mutineer.yml` keys.

+ - [Ruby mutation-testing tools compared](https://davidteren.github.io/mutineer/comparison.md): Mutineer, Mutant, and other Ruby tools, plus a fit-check prompt for your coding agent.

- [JSON report schema](https://davidteren.github.io/mutineer/json-schema.html): the versioned JSON contract — `summary`, `survivors[]`, `no_coverage[]`, `uncapturable[]`, `unplaceable[]`, `ran_at_load[]`, `no_verdict[]`, `ignored[]`, `per_source[]`, and the `baseline` and `matrix` blocks.

- [Ruby API (YARD)](https://davidteren.github.io/mutineer/api/): class reference generated from the website build’s source revision.

- [Sample HTML report](https://davidteren.github.io/mutineer/sample-report.html): example report data displayed in the website theme; the CLI’s self-contained HTML output has a different presentation.

## Source & packages

- [GitHub repository](https://github.com/davidteren/mutineer): source, issues, `AGENTS.md`, and `CHANGELOG.md`.

- [RubyGems package](https://rubygems.org/gems/mutineer): `gem install mutineer`.

- [GitHub Marketplace action](https://github.com/marketplace/actions/mutineer-ruby): drop-in PR mutation gate.

## Optional

- - [Full docs as one file](https://davidteren.github.io/mutineer/llms-full.txt): README + agent/CI guide + JSON schema concatenated for LLM ingestion.

+ - [Full docs as one file](https://davidteren.github.io/mutineer/llms-full.txt): README + agent/CI guide + user guides + JSON schema concatenated for LLM ingestion.

- [Agent skill](https://davidteren.github.io/mutineer/skill.md): compact skill card — install, the agent loop, exit codes, and links.

- [Landing page (Markdown)](https://davidteren.github.io/mutineer/index.md): homepage / CLI essentials twin of the HTML landing page.

- [Mutation testing, explained (Markdown)](https://davidteren.github.io/mutineer/learn.md): Markdown twin of the beginner guide.

- [Agent & CI guide (Markdown)](https://davidteren.github.io/mutineer/agentic-coding.md): Markdown twin of the agent inner-loop and CI recipes.

- [Equivalent skips (Markdown)](https://davidteren.github.io/mutineer/equivalent-skips.md): Markdown twin of the built-in equivalent-skip list.

- [Rails rollout (Markdown)](https://davidteren.github.io/mutineer/rails.md): Markdown twin of the Rails rollout guide.

- [JSON schema (Markdown)](https://davidteren.github.io/mutineer/json-schema.md): Markdown twin of the JSON report schema reference.

- [Agent access policy](https://davidteren.github.io/mutineer/agents.txt): read-only access policy and pointers at `llms.txt` / `sitemap.xml`.