Agent skill

Mutation Testing

Configures mewt or muton mutation testing campaigns — scopes targets, tunes timeouts, and optimizes long-running runs.

MITAuto-check: notesTesting & QA

Install Mutation Testing

skills CLI

$ npx skills add CraftOS-dev/CraftBot --skill mutation-testing -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install CraftOS-dev/CraftBot mutation-testing --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/mutation-testing .claude/skills/mutation-testing && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "mutation-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/mutation-testing into .claude/skills/mutation-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-testing", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/CraftOS-dev/CraftBot/tree/main/skills/mutation-testing

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add CraftOS-dev/CraftBot --skill mutation-testing -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install CraftOS-dev/CraftBot mutation-testing --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/mutation-testing .agents/skills/mutation-testing && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "mutation-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/mutation-testing into .agents/skills/mutation-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-testing", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add CraftOS-dev/CraftBot --skill mutation-testing -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install CraftOS-dev/CraftBot mutation-testing --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/mutation-testing .cursor/skills/mutation-testing && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "mutation-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/mutation-testing into .cursor/skills/mutation-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-testing", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/CraftOS-dev/CraftBot.git --path skills/mutation-testing

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add CraftOS-dev/CraftBot --skill mutation-testing -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install CraftOS-dev/CraftBot mutation-testing --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/mutation-testing .gemini/skills/mutation-testing && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "mutation-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/mutation-testing into .gemini/skills/mutation-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-testing", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install CraftOS-dev/CraftBot mutation-testing

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add CraftOS-dev/CraftBot --skill mutation-testing -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/mutation-testing .github/skills/mutation-testing && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "mutation-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/mutation-testing into .github/skills/mutation-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-testing", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add CraftOS-dev/CraftBot --skill mutation-testing -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install CraftOS-dev/CraftBot mutation-testing --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/CraftOS-dev/CraftBot.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/mutation-testing .opencode/skills/mutation-testing && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "mutation-testing" agent skill from https://github.com/CraftOS-dev/CraftBot/tree/main/skills/mutation-testing into .opencode/skills/mutation-testing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-testing", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: mutation-testing
GitHub stars: 392
Token cost: ~713 tokens
SKILL.md length: 203 words
Files: 3 (incl. references)
Skills in repo: 89
Repo updated: Oct 7, 2026
First seen: Oct 7, 2026
Licence: MIT

At a glance

Configures mewt or muton mutation testing campaigns — scopes targets, tunes timeouts, and optimizes long-running runs.

The user mentions mewt
SKILL.md covers When to Use, When NOT to Use, Quick Start and Reference Index, plus 2 more sections
Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
Mutation testing

What it does

Mutation Testing is an agent skill from CraftOS-dev/CraftBot. Configures mewt or muton mutation testing campaigns — scopes targets, tunes timeouts, and optimizes long-running runs. Use when the user mentions mewt, muton, mutation testing, or wants to configure or optimize a mutation testing campaign.

Its SKILL.md is about 710 tokens, which your agent loads only when the skill is triggered. The skill folder holds 4 other files, including reference files (for example `references/optimization-strategies.md` and `workflows/configuration.md`).

It sits in Testing & QA, covering Test coverage. The repository describes itself as: One agent. Every kind of work. The licence is MIT.

When your agent uses it

The user mentions mewt
Mutation testing
Wants to configure
Optimize a mutation testing campaign

Example prompts

“Use the mutation-testing skill to configure mewt or muton mutation testing campaigns — scopes targets, tunes timeouts, and optimizes long-running runs”
“/mutation-testing”

Requirements

Pre-approved tools (allowed-tools): Read, Write, Bash, Grep

What it can do on your machine

Read from SKILL.md and the folder at commit b50970c. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves these tools, so the agent can use them without asking each time:
- Read
- Write
- Bash
- Grep
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md (its code samples are bash).
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Mutation Testing loads about 713 tokens when it runs, and up to ~2.9k if it reads all its reference files. Until then it costs about 64 tokens; SKILL.md has 203 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~64
When it runs · the whole SKILL.md, loaded when a task matches: ~713
With references · SKILL.md plus every file in references/, read only if the agent opens them: ~2.9k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check: notes

The automated check noted patterns worth knowing about, such as sudo or a known installer.

NotePre-approves every shell command (allowed-tools: Bash)SKILL.md
```
allowed-tools: Read, Write, Bash, Grep
```

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from CraftOS-dev/CraftBot at commit b50970c, republished under its MIT licence (© CraftOS-dev). 203 words, ~713 tokens.

Download SKILL.mdSave it as .claude/skills/mutation-testing/SKILL.md (or your agent's skills folder). This skill also uses 2 other files; get the full folder from GitHub.

name: mutation-testing
description: Configures mewt or muton mutation testing campaigns — scopes targets, tunes timeouts, and optimizes long-running runs. Use when the user mentions mewt, muton, mutation testing, or wants to configure or optimize a mutation testing campaign.
allowed-tools: Read, Write, Bash, Grep

Mutation Testing — Campaign Configuration (mewt/muton)

Note: muton and mewt share identical interfaces but target different languages — mewt for general-purpose languages (Rust, Solidity, Go, TypeScript, JavaScript), muton for TON smart contracts (Tact, Tolk, FunC). All examples use mewt commands, but they work exactly the same with muton. File names change accordingly: mewt.toml → muton.toml, mewt.sqlite → muton.sqlite.

When to Use

Use this skill when the user:

Mentions "mewt", "muton", or "mutation testing"
Needs to configure or optimize a mutation testing campaign
Wants to run mewt run and needs help getting set up first

When NOT to Use

Do not use this skill when the user:

Wants to analyze or report on completed campaign results
Asks about tests or coverage without mentioning mutation testing

Quick Start

Load workflows/configuration.md — a 5-phase guide from mewt init to a validated, ready-to-run campaign.

General question or unfamiliar command? Run mewt --help or mewt <subcommand> --help, then assist.

Reference Index

File	Content
workflows/configuration.md	5-phase guide: init, scope, optimize, validate, run
references/optimization-strategies.md	Per-file targeting, two-phase campaigns, mutation type filtering

Essential Commands

bash

# Initialize and mutate
mewt init                    # Create mewt.toml and mewt.sqlite
mewt mutate [paths]          # Generate mutants without running tests
mewt run [paths]             # Run the full campaign

# Inspect configuration and scope
mewt print config            # View effective configuration
mewt print targets           # Table of all targeted files
mewt print mutations --language [lang]  # Available mutation types
mewt status                  # Mutant count and per-file breakdown

# Investigate specific mutants
mewt print mutants --target [path]   # All mutants for a file
mewt print mutants --severity high   # Filter by severity
mewt print mutant --id [id]          # View mutated code diff
mewt test --ids [ids]                # Re-test specific mutants

What Results Mean

Caught/TestFail: Tests detected the mutation (good)
Uncaught: Mutation survived — indicates untested logic
Timeout: Tests took too long, inconclusive
Skipped: A more severe mutant already failed on the same line

Files

SKILL.md and 2 other files (references) in skills/mutation-testing of CraftOS-dev/CraftBot.

SKILL.md
references/optimization-strategies.md
workflows/configuration.md

Open the folder on GitHubat commit b50970c

Compare with similar skills

Mutation Testing next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Mutation Testing compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
Mutation Testing this skillCraftOS-dev/CraftBot	392	—	~713	Automated safety check: Notes	MIT	today
Requirementsrizsotto/Bear	6.5k	—	~2k	Automated safety check: Pass	GPL-3.0	today
Crap Analysisardalis/RiverBooks	134	2 repos	~3.4k	Automated safety check: Pass	None	yesterday
Code Coverages3s-project/s3s	311	—	~789	Automated safety check: Pass	Apache-2.0	today
Project Statusbactopia/bactopia	522	—	~787	Automated safety check: Pass	MIT	2 mo ago
Check Coverageldayton/Dippy	243	—	~403	Automated safety check: Pass	MIT	3 mo ago

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Questions about Mutation Testing

What does Mutation Testing do?

Configures mewt or muton mutation testing campaigns — scopes targets, tunes timeouts, and optimizes long-running runs. Mutation Testing is an agent skill from CraftOS-dev/CraftBot. Configures mewt or muton mutation testing campaigns — scopes targets, tunes timeouts, and optimizes long-running runs.

When should I use Mutation Testing?

Mutation Testing fits situations like: the user mentions mewt; mutation testing; wants to configure; optimize a mutation testing campaign.

How do I install Mutation Testing in Claude Code?

Run `npx skills add CraftOS-dev/CraftBot --skill mutation-testing -a claude-code`. Or copy the skill folder (skills/mutation-testing in CraftOS-dev/CraftBot) into .claude/skills/mutation-testing in your project. Claude Code loads it when a task matches its description.

How do I install Mutation Testing in Codex?

Run `npx skills add CraftOS-dev/CraftBot --skill mutation-testing -a codex`. Or copy the skill folder (skills/mutation-testing in CraftOS-dev/CraftBot) into .agents/skills/mutation-testing in your project. Codex loads it when a task matches its description.

Can I use Mutation Testing in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add CraftOS-dev/CraftBot --skill mutation-testing -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/mutation-testing, .gemini/skills/mutation-testing, .github/skills/mutation-testing and .opencode/skills/mutation-testing in your project.

What does Mutation Testing need to run?

SKILL.md names no scripts, command-line tools or credentials: Mutation Testing is instructions for the agent only. Its frontmatter pre-approves these tools: Read, Write, Bash, Grep.

Does Mutation Testing access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Mutation Testing safe to install?

Our automated static check of SKILL.md found notes only (pre-approves every shell command (allowed-tools: bash)), nothing it rates as a warning. It is not a guarantee. Review the folder before installing.

What licence does Mutation Testing use?

Mutation Testing is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Mutation Testing use?

About 713 tokens (SKILL.md is roughly 2.9k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 2.1k tokens, read only when the agent opens those files.

What are the alternatives to Mutation Testing?

Skills that share tags, products or a category with Mutation Testing: Requirements (rizsotto/Bear, 6.5k stars), Crap Analysis (ardalis/RiverBooks, 134 stars), Code Coverage (s3s-project/s3s, 311 stars) and Project Status (bactopia/bactopia, 522 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Mutation Testing?

CraftOS-dev (a GitHub user) maintains it in CraftOS-dev/CraftBot, which has 392 GitHub stars. The repository holds 89 skills in this directory. The repository was last updated on October 7, 2026.

Source: CraftOS-dev/CraftBot on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Mutation Testing

Install Mutation Testing

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Mutation Testing — Campaign Configuration (mewt/muton)

When to Use

When NOT to Use

Quick Start

Reference Index

Essential Commands

What Results Mean

Files

Compare with similar skills

Similar skills

Requirements

Crap Analysis

Code Coverage

Project Status

Check Coverage

Guarding Destructive Operations

More from CraftOS-dev/CraftBot

Self Improvement

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Outlook

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Questions about Mutation Testing

Install Mutation Testing

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Mutation Testing — Campaign Configuration (mewt/muton)

When to Use

When NOT to Use

Quick Start

Reference Index

Essential Commands

What Results Mean

Files

Compare with similar skills

Similar skills

More from CraftOS-dev/CraftBot

Related

Questions about Mutation Testing