Mutation Test Runner
Mutation testing to validate test quality by introducing code changes and verifying tests catch them
- Type
- Plugin
- Repository
- jeremylongshore/tons-of-skills-marketplace
- GitHub stars
- 2.8k
- License
- MIT
- Repo last updated
- Sep 27, 2026
- Version
- 1.27.0
- Author
- Claude Code Plugins
What Mutation Test Runner is
Mutation Test Runner is a plugin published in the jeremylongshore/tons-of-skills-marketplace repository on GitHub, which has about 2.8k stars. The repository describes itself as: “Model-agnostic agent-skills platform with a harness-free canonical layer, verified adapters, and the ccpi package manager. Explore at tonsofskills.com.”
A plugin is a package that bundles skills, slash commands, subagents, hooks, and MCP connectors so they install together. Plugins are plain files with a manifest at .claude-plugin/plugin.json, and they work in both Claude Code and Claude Cowork.
Installing Mutation Test Runner adds everything it ships in one step. Connectors inside a plugin still need to be connected separately, and hooks and subagents only run in Cowork and Claude Code, not in regular chat.
How to install Mutation Test Runner
Claude Code
- Add the repository as a plugin marketplace: claude plugin marketplace add jeremylongshore/tons-of-skills-marketplace
- Install the plugin: claude plugin install mutation-test-runner@<marketplace-name>, using the marketplace name from the repository's .claude-plugin/marketplace.json.
- Restart the session if the new skills or commands don't appear straight away.
Claude Cowork
- Open Customize → Plugins and choose Add marketplace.
- Enter jeremylongshore/tons-of-skills-marketplace (the owner/repo shorthand works for GitHub).
- Find Mutation Test Runner in the list, click Install, then connect any connectors it needs from its Connectors tab.
New to extending Cowork? Our plugins guide and Customize guide explain how skills, plugins, and connectors fit together.
Inside the source file
An excerpt from plugins/testing/mutation-test-runner/.claude-plugin/plugin.json, shared under the repository's MIT license. Read the full file on GitHub.
Validate test suite effectiveness through mutation testing - introducing code changes and verifying tests catch them.
Features
- Mutation generation - Arithmetic, logical, conditional mutations
- Test validation - Verify tests catch introduced bugs
- Mutation score calculation - Test quality metric
- Survivor analysis - Identify weak test coverage
- Framework support - Stryker, PITest, mutmut, Mutant
Installation
/plugin install mutation-test-runner@claude-code-plugins-plusUsage
Run mutation testing on the validator module
Analyze mutation test results and suggest improvementsMutation Types
- Arithmetic - + → -, * → /
- Comparison - > → >=, == → !=
- Logical - && → ||, ! removal
- Boolean - true → false
- Conditionals - Remove if statements
License
MIT
Before you install
- Read the whole file first. Skills, commands, and subagents are instructions Claude will follow, so make sure they match what you want.
- Check which tools, scripts, or MCP servers it uses. Local servers and scripts run with your permissions.
- Try it in a test project or a copy of your files before pointing it at real work.
- Pin the version you tested, and review changes before updating.
- Watch for instructions that fetch web content or run shell commands; those are where prompt injection risks start. See our prompt injection guide.
FAQ
What is Mutation Test Runner?
Mutation Test Runner is a plugin for Claude Code and Claude Cowork from the jeremylongshore/tons-of-skills-marketplace repository on GitHub. Mutation testing to validate test quality by introducing code changes and verifying tests catch them
How do I install Mutation Test Runner in Claude Code?
Add the repository as a plugin marketplace: claude plugin marketplace add jeremylongshore/tons-of-skills-marketplace Install the plugin: claude plugin install mutation-test-runner@<marketplace-name>, using the marketplace name from the repository's .claude-plugin/marketplace.json. Restart the session if the new skills or commands don't appear straight away.
Can I use Mutation Test Runner in Claude Cowork?
Open Customize → Plugins and choose Add marketplace. Enter jeremylongshore/tons-of-skills-marketplace (the owner/repo shorthand works for GitHub). Find Mutation Test Runner in the list, click Install, then connect any connectors it needs from its Connectors tab.
Is Mutation Test Runner safe to install?
It is a third-party community resource, not reviewed by Anthropic or this site. Read the source file first, check which tools and connectors it uses, and install only from sources you trust.
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