mutation-testing · trailofbits — Claude Code skill: mutation testing campaigns
A skill that walks the agent through mutation testing: setting up a mewt or muton campaign, reading surviving mutants, hunting bugs in untested code.
npx skills add trailofbits/skills --skill mutation-testing -a claude-codeWhat mutation-testing does
The skill does not run mutation testing itself. It picks the right workflow and loads the reference files that workflow needs. There are three paths: configuring or speeding up a campaign, hunting bugs in code the tests miss, and turning results into a formal report. Each path lists what else to read, such as the equivalence catalog or the report template.
It covers both mewt and muton, which share the same interface but use different config and database files (mewt.toml versus muton.toml). The blockchain reference loads only for Solidity, Move, FunC/Tolk, Cairo and Solana Rust targets. Results from another tool get a separate input-format reference.
The skill can read files, write, run shell commands and grep code — Read Write Bash Grep. It does not pin down flag behavior: mewt --help is treated as the source of truth, so an unfamiliar flag sends the agent to the help output. Check your mewt version against the 4.x examples before starting a campaign.
What it helps with
- scope a mutation testing campaign to specific paths
- trim a campaign whose estimate runs too long
- sort surviving mutants into real test gaps and equivalent mutations
- find bugs in code that tests never exercise
- produce a formal report with severity tiers
Example prompts for the agent
- Set up a mutation testing campaign for
src/auth/**and tell me how long it will take - Go through the surviving mutants from the last run: which are test gaps and which are equivalent mutations
- Write up the campaign results as a report grouped by severity
How to install mutation-testing
1Skills CLI (Vercel)
npx skills add trailofbits/skills --skill mutation-testing -a claude-code2Manually: put the files in place
~/.claude/skills/mutation-testing/SKILL.mdCopy the whole skill folder; for one project use .claude/skills/mutation-testing/
1Skills CLI (Vercel)
npx skills add trailofbits/skills --skill mutation-testing -a codex2Manually: put the files in place
.agents/skills/mutation-testing/SKILL.mdFor all projects use ~/.agents/skills/
1Skills CLI (Vercel)
npx skills add trailofbits/skills --skill mutation-testing -a cursor2Manually: put the files in place
.cursor/skills/mutation-testing/SKILL.mdCursor also reads .agents/skills/ and .claude/skills/
1GitHub CLI
gh skill install trailofbits/skills mutation-testing2Manually: put the files in place
.github/skills/mutation-testing/SKILL.md1Skills CLI (Vercel)
npx skills add trailofbits/skills --skill mutation-testing -a gemini-cli2Platform CLI
gemini skills install https://github.com/trailofbits/skills --path plugins/mutation-testing/skills/mutation-testingManually: put the files in place
.devin/skills/mutation-testing/SKILL.mdThe legacy .windsurf/skills/ path still works
Skills CLI (Vercel)
npx skills add trailofbits/skills --skill mutation-testing -a opencodeClaude.ai
Zip the folder and upload it in Settings → Capabilities → Skills
Step by step, with commands for each platform: How to install skills in Claude Code: five ways
Questions about mutation-testing
How do I install mutation-testing in Claude Code?
Run npx skills add trailofbits/skills --skill mutation-testing -a claude-code. The skill lands at ~/.claude/skills/mutation-testing/SKILL.md.
What does the mutation-testing skill do?
It chooses one of three mutation testing workflows — campaign setup, bug hunting, or reporting — and loads the matching references. The agent then works with mewt or muton on your paths and results.
How do mewt and muton differ here?
Their interfaces match; the file names do not. A muton project uses muton.toml and muton.sqlite, while the examples in the skill are written for mewt 4.x.
Similar skills
Everything for Testing and QA →mutation-testing by other authors comes first.
