Guidelines
akash-network/node
Behavioral guidelines to reduce common LLM coding mistakes. An agent skill from akash-network/node.
Run cargo-mutants for changed coop logic and keep .cargo/mutants.toml synchronized.
Install Mutation Check
$ npx skills add trailofbits/coop --skill mutation-check -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install trailofbits/coop mutation-check --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/trailofbits/coop.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/mutation-check .claude/skills/mutation-check && rm -rf skills-srcUse ~/.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/
Install the "mutation-check" agent skill from https://github.com/trailofbits/coop/tree/main/.agents/skills/mutation-check into .claude/skills/mutation-check/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-check", 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 install https://github.com/trailofbits/coop/tree/main/.agents/skills/mutation-checkType 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.
$ npx skills add trailofbits/coop --skill mutation-check -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install trailofbits/coop mutation-check --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/trailofbits/coop.git skills-src && mkdir -p .agents/skills && cp -r skills-src/.agents/skills/mutation-check .agents/skills/mutation-check && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "mutation-check" agent skill from https://github.com/trailofbits/coop/tree/main/.agents/skills/mutation-check into .agents/skills/mutation-check/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-check", 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.
$ npx skills add trailofbits/coop --skill mutation-check -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install trailofbits/coop mutation-check --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/trailofbits/coop.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/.agents/skills/mutation-check .cursor/skills/mutation-check && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "mutation-check" agent skill from https://github.com/trailofbits/coop/tree/main/.agents/skills/mutation-check into .cursor/skills/mutation-check/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-check", 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 https://github.com/trailofbits/coop.git --path .agents/skills/mutation-check--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add trailofbits/coop --skill mutation-check -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install trailofbits/coop mutation-check --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/trailofbits/coop.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/.agents/skills/mutation-check .gemini/skills/mutation-check && rm -rf skills-srcUse ~/.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/
Install the "mutation-check" agent skill from https://github.com/trailofbits/coop/tree/main/.agents/skills/mutation-check into .gemini/skills/mutation-check/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-check", 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.
$ gh skill install trailofbits/coop mutation-checkInstalls 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).
$ npx skills add trailofbits/coop --skill mutation-check -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/trailofbits/coop.git skills-src && mkdir -p .github/skills && cp -r skills-src/.agents/skills/mutation-check .github/skills/mutation-check && rm -rf skills-srcUse ~/.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/
Install the "mutation-check" agent skill from https://github.com/trailofbits/coop/tree/main/.agents/skills/mutation-check into .github/skills/mutation-check/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-check", 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.
$ npx skills add trailofbits/coop --skill mutation-check -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install trailofbits/coop mutation-check --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/trailofbits/coop.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/.agents/skills/mutation-check .opencode/skills/mutation-check && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "mutation-check" agent skill from https://github.com/trailofbits/coop/tree/main/.agents/skills/mutation-check into .opencode/skills/mutation-check/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "mutation-check", 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-check- GitHub stars
- 762
- Token cost
- ~389 tokens
- SKILL.md length
- 177 words
- Files
- 1
- Skills in repo
- 6
- Repo updated
- First seen
- Licence
- Apache-2.0
At a glance
Run cargo-mutants for changed coop logic and keep .cargo/mutants.toml synchronized.
- Works in 5 steps: Inspect the diff before running. New… → Sanity-check changed exclusions with… → Run a full-file sweep for each touched… → …
- Logic-dense modules change
- Calls cargo
- Before refactors
What it does
Mutation Check is an agent skill from trailofbits/coop, published by the product's own GitHub organization. Run cargo-mutants for changed coop logic and keep .cargo/mutants.toml synchronized. Use when logic-dense modules change, before refactors, or when asked to verify mutation coverage.
Its SKILL.md is about 390 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.
It sits in Development, covering Refactoring. The repository describes itself as: Isolated VM environment for running Claude Code and Codex. The licence is Apache-2.0.
When your agent uses it
- Logic-dense modules change
- Before refactors
- Asked to verify mutation coverage
Example prompts
- “/mutation-check”
Workflow steps
5 steps, taken from the first numbered list in SKILL.md.
- Inspect the diff before running. New functions in logic modules that shell
- Sanity-check changed exclusions with cargo mutants --list -f .
- Run a full-file sweep for each touched scoped module and library tests only
- Triage mutants.out/missed.txt: add a discriminating test for real gaps,
- Report files swept, missed count before/after, every survivor's disposition,
What it can do on your machine
Read from SKILL.md and the folder at commit 0f1c4ef. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
Shell commands in SKILL.md call:
cargo
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 Check loads about 389 tokens when it runs. Until then it costs about 49 tokens; SKILL.md has 177 words of instructions outside code blocks.
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 passed
The automated check found no risky patterns in SKILL.md.
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 trailofbits/coop at commit 0f1c4ef, republished under its Apache-2.0 licence (© trailofbits). 177 words, ~389 tokens.
Download SKILL.mdSave it as
.claude/skills/mutation-check/SKILL.md (or your agent's skills folder).- name
- mutation-check
- description
- Run cargo-mutants for changed coop logic and keep .cargo/mutants.toml synchronized. Use when logic-dense modules change, before refactors, or when asked to verify mutation coverage.
Mutation Check
Read docs/testing.md first.
- Inspect the diff before running. New functions in logic modules that shell
out, drive
&PlatformBackend, read a TTY, or write stdout must be excluded in.cargo/mutants.tomlin the same PR. Extract and test their pure decision logic. Pure helpers remain in scope. - Sanity-check changed exclusions with
cargo mutants --list -f <file>. - Run a full-file sweep for each touched scoped module and library tests only:
cargo mutants -f src/<file>.rs -- --lib. Redirect output to a file; do not pipe a long run throughheadorgrep. - Triage
mutants.out/missed.txt: add a discriminating test for real gaps, mark genuinely equivalent mutants with a narrow documented skip, and delete dead code. Confirm each new test by re-running the mutant or deliberately breaking the protected behavior. - Report files swept, missed count before/after, every survivor's disposition,
and whether
.cargo/mutants.tomlchanged.
Do not spend a full mutation run on whole-module exclusions (backend.rs,
lima.rs, setup.rs, update.rs, ssh.rs, vm.rs, network.rs,
port_forward.rs, cmd.rs, prompt.rs, main.rs). Instead, identify the
unit/integration blind spot explicitly and test extracted pure logic directly.
© trailofbits, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
Just SKILL.md in .agents/skills/mutation-check of trailofbits/coop.
Open the folder on GitHubat commit 0f1c4ef
Compare with similar skills
Mutation Check 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.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Mutation Check this skilltrailofbits/coop | 762 | — | ~389 | Automated safety check: Pass | Apache-2.0 | |
| Guidelinesakash-network/node | 1.1k | 22 repos | ~577 | Automated safety check: Pass | MIT | |
| Component Refactoringlangflow-ai/langflow | 156k | — | ~3.5k | Automated safety check: Pass | MIT | |
| Migrate Core Code to Submodulestinyhumansai/openhuman | 41k | — | ~2.6k | Automated safety check: Pass | GPL-3.0 | |
| ast-grep Structural Searchcode-yeongyu/oh-my-openagent | 70k | — | ~3.3k | Automated safety check: Pass | MIT | |
| Systematic Code Refactoringluongnv89/claude-howto | 42k | — | ~3k | Automated safety check: Pass | MIT |
Similar skills
Component Refactoring
langflow-ai/langflow
Refactor high-complexity React components in Langflow frontend.
Migrate Core Code to Submodules
tinyhumansai/openhuman
Plans and carries out moving non-host-specific code and its tests from the OpenHuman core into vendored tiny submodule libraries, then releases the submodule and re-pins the host.
ast-grep Structural Search
code-yeongyu/oh-my-openagent
Searches and rewrites code by syntax-tree shape across 25 languages with ast-grep, for codemods, structural queries and YAML lint rules, using a Python wrapper script.
Systematic Code Refactoring
luongnv89/claude-howto
Guides refactoring in phases based on Martin Fowler's method: research, test coverage check, planning and small tested steps, with your approval at each phase.
Codex
skills-directory/skill-codex
A skill your agent uses when the user asks to run Codex CLI (codex exec, codex resume) or references OpenAI Codex for code analysis, refactoring, or automated editing
More from trailofbits/coop
- Official
Closeout Review
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Run the final scope-controlled review before committing, pushing, or opening a PR.
- Official
Review
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Review a coop pull request or local diff with independent, self-validated correctness, design, convention, security, API, test, documentation, and comment lenses.
- Official
Babysit PR
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Shepherd the current user's open PR through base updates, CI failures, and review feedback without rewriting history or merging.
- Official
Babysit My PRs
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Triage and shepherd all open PRs owned by the current GitHub user, isolating each writable worker in its own worktree.
- Official
Integration
trailofbits/coop
Run and interpret coop's VM integration suite locally on Lima or remotely on Firecracker.
Related
Categories
Questions about Mutation Check
What does Mutation Check do?
Run cargo-mutants for changed coop logic and keep .cargo/mutants.toml synchronized. Mutation Check is an agent skill from trailofbits/coop, published by the product's own GitHub organization.toml synchronized.
When should I use Mutation Check?
Mutation Check fits situations like: logic-dense modules change; before refactors; asked to verify mutation coverage.
How do I install Mutation Check in Claude Code?
Run `npx skills add trailofbits/coop --skill mutation-check -a claude-code`. Or copy the skill folder (.agents/skills/mutation-check in trailofbits/coop) into .claude/skills/mutation-check in your project. Claude Code loads it when a task matches its description.
How do I install Mutation Check in Codex?
Run `npx skills add trailofbits/coop --skill mutation-check -a codex`. Or copy the skill folder (.agents/skills/mutation-check in trailofbits/coop) into .agents/skills/mutation-check in your project. Codex loads it when a task matches its description.
Can I use Mutation Check 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 trailofbits/coop --skill mutation-check -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-check, .gemini/skills/mutation-check, .github/skills/mutation-check and .opencode/skills/mutation-check in your project.
What does Mutation Check need to run?
Going by SKILL.md and its folder, Mutation Check needs the command-line tools its instructions call (cargo).
Does Mutation Check 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 Check safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Mutation Check use?
Mutation Check is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Mutation Check use?
About 389 tokens (SKILL.md is roughly 1.6k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.
What are the alternatives to Mutation Check?
Skills that share tags, products or a category with Mutation Check: Guidelines (akash-network/node, 1.1k stars), Component Refactoring (langflow-ai/langflow, 156k stars), Migrate Core Code to Submodules (tinyhumansai/openhuman, 41k stars) and ast-grep Structural Search (code-yeongyu/oh-my-openagent, 70k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Mutation Check?
trailofbits (a GitHub organization, an official publisher) maintains it in trailofbits/coop, which has 762 GitHub stars. The repository holds 6 skills in this directory. The repository was last updated on October 7, 2026.
Source: trailofbits/coop on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.