Check npm
grafana/skills
Audit a JavaScript/TypeScript repo's npm, yarn, or pnpm configuration for supply-chain hardening: tool version, lifecycle scripts, unsafe dependency protocols, and minimum release age ≥3 days.
Introduce StrykerJS mutation testing or assess JavaScript/TypeScript test quality.
Install Stryker JS
$ npx skills add mizchi/skills --skill stryker-js -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install mizchi/skills stryker-js --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/mizchi/skills.git skills-src && mkdir -p .claude/skills && cp -r skills-src/stryker-js .claude/skills/stryker-js && 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 "stryker-js" agent skill from https://github.com/mizchi/skills/tree/main/stryker-js into .claude/skills/stryker-js/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "stryker-js", 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/mizchi/skills/tree/main/stryker-jsType 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 mizchi/skills --skill stryker-js -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install mizchi/skills stryker-js --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/mizchi/skills.git skills-src && mkdir -p .agents/skills && cp -r skills-src/stryker-js .agents/skills/stryker-js && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "stryker-js" agent skill from https://github.com/mizchi/skills/tree/main/stryker-js into .agents/skills/stryker-js/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "stryker-js", 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 mizchi/skills --skill stryker-js -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install mizchi/skills stryker-js --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/mizchi/skills.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/stryker-js .cursor/skills/stryker-js && 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 "stryker-js" agent skill from https://github.com/mizchi/skills/tree/main/stryker-js into .cursor/skills/stryker-js/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "stryker-js", 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/mizchi/skills.git --path stryker-js--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 mizchi/skills --skill stryker-js -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install mizchi/skills stryker-js --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/mizchi/skills.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/stryker-js .gemini/skills/stryker-js && 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 "stryker-js" agent skill from https://github.com/mizchi/skills/tree/main/stryker-js into .gemini/skills/stryker-js/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "stryker-js", 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 mizchi/skills stryker-jsInstalls 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 mizchi/skills --skill stryker-js -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/mizchi/skills.git skills-src && mkdir -p .github/skills && cp -r skills-src/stryker-js .github/skills/stryker-js && 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 "stryker-js" agent skill from https://github.com/mizchi/skills/tree/main/stryker-js into .github/skills/stryker-js/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "stryker-js", 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 mizchi/skills --skill stryker-js -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install mizchi/skills stryker-js --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/mizchi/skills.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/stryker-js .opencode/skills/stryker-js && 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 "stryker-js" agent skill from https://github.com/mizchi/skills/tree/main/stryker-js into .opencode/skills/stryker-js/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "stryker-js", 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
stryker-js- GitHub stars
- 359
- Token cost
- ~2.4k tokens
- SKILL.md length
- 833 words
- Files
- 17 (incl. references, assets)
- Skills in repo
- 69
- Repo updated
- First seen
- Licence
- None found
At a glance
Introduce StrykerJS mutation testing or assess JavaScript/TypeScript test quality.
- Works in 4 steps: Establish that the original tests pass.… → Read the report, source, relevant tests… → Add a focused regression or a property… → …
- Tasks that involve Test coverage
- SKILL.md covers Choose the work, CI and local scope, Local AI feedback loop and Interpretation, plus 2 more sections
- Runs JavaScript and TypeScript scripts from its folder; calls pnpm and just
What it does
Stryker JS is an agent skill from mizchi/skills. Introduce StrykerJS mutation testing or assess JavaScript/TypeScript test quality. Use Git diff mutations in CI and surviving mutants locally to find missing cases and weak assertions, including tests generated by AI.
Its SKILL.md is about 2.4k tokens, which your agent loads only when the skill is triggered. The skill folder holds 21 other files, including reference files and assets (for example `README.md`, `assets/examples/shipping.test.ts` and `assets/examples/shipping.ts`).
It sits in Testing & QA, covering Test coverage. It works with Git, JavaScript, TypeScript and pnpm. The repository describes itself as: Agent skills by mizchi, distributed via APM.
When your agent uses it
- Tasks that involve Test coverage
Example prompts
- “/stryker-js”
Requirements
- Node.js
Workflow steps
4 steps, taken from the first numbered list in SKILL.md.
- Establish that the original tests pass. Select the behavioral module under review and run Stryker with HTML and JSON output. Record the…
- Read the report, source, relevant tests and specification. For each meaningful Survived or NoCoverage result, identify the smallest legal…
- Add a focused regression or a property using an independent oracle. The original must pass; the relevant mutant must fail. Improve…
- Rerun the module and summarize the result. If a supplied score target is unmet, continue fixing demonstrated gaps until it is met or a…
What it can do on your machine
Read from SKILL.md and the folder at commit 62f5808. 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
Ships script files (JavaScript and TypeScript, from the files we listed), which the agent can run.
Shell commands in SKILL.md call:
pnpmjust
From the folder's file list and the shell code blocks in SKILL.md.
Network
Links to these hosts (documentation or services it may open):
stryker-mutator.iogithub.com
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
Stryker JS loads about 2.4k tokens when it runs, and up to ~5.9k if it reads all its reference files. Until then it costs about 57 tokens; SKILL.md has 833 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
Without a licence we can't republish the file, so here is its outline and opening line. It has 833 words (~2,446 tokens).
“Use mutation testing to ask whether tests detect plausible defects in production code. A passing suite or high coverage alone does not answer that question. Mutate production source; improve the tests that fail to detect meaningful mutations.”
- name
- stryker-js
Files
SKILL.md and 16 other files (references, assets) in stryker-js of mizchi/skills.
- SKILL.md
- README.md
- assets/examples/shipping.test.ts
- assets/examples/shipping.ts
- assets/gitignore.snippet
- assets/justfile
- assets/mutation-diff.yml
- assets/package.scripts.json
- assets/patches/vitest-runner-10-vitest-5.patch
- assets/scripts/mutation-changed.mjs
- assets/scripts/mutation-plan.mjs
- assets/scripts/mutation-summary.mjs
- assets/stryker.config.json
- references/evaluate-tests.md
- references/setup.md
- tests
- … and 1 more
Open the folder on GitHubat commit 62f5808
Compare with similar skills
Stryker JS 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 |
|---|---|---|---|---|---|---|
| Stryker JS this skillmizchi/skills | 359 | — | ~2.4k | Automated safety check: Pass | None | |
| Check npmgrafana/skills | 281 | — | ~1.3k | Automated safety check: Warn | Apache-2.0 | |
| Apprunyysun/apprun | 1.2k | — | ~1.3k | Automated safety check: Pass | MIT | |
| E2E Testcrowdin/crowdin-api-client-js | 139 | — | ~893 | Automated safety check: Notes | MIT | |
| Supercovsupercorp-ai/supercov | 151 | 1 repos | ~415 | Automated safety check: Pass | MIT | |
| Supercov Securitysupercorp-ai/supercov | 151 | 1 repos | ~236 | Automated safety check: Pass | MIT |
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Questions about Stryker JS
What does Stryker JS do?
Introduce StrykerJS mutation testing or assess JavaScript/TypeScript test quality. Stryker JS is an agent skill from mizchi/skills. Introduce StrykerJS mutation testing or assess JavaScript/TypeScript test quality.
When should I use Stryker JS?
Stryker JS fits situations like: tasks that involve Test coverage.
How do I install Stryker JS in Claude Code?
Run `npx skills add mizchi/skills --skill stryker-js -a claude-code`. Or copy the skill folder (stryker-js in mizchi/skills) into .claude/skills/stryker-js in your project. Claude Code loads it when a task matches its description.
How do I install Stryker JS in Codex?
Run `npx skills add mizchi/skills --skill stryker-js -a codex`. Or copy the skill folder (stryker-js in mizchi/skills) into .agents/skills/stryker-js in your project. Codex loads it when a task matches its description.
Can I use Stryker JS 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 mizchi/skills --skill stryker-js -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/stryker-js, .gemini/skills/stryker-js, .github/skills/stryker-js and .opencode/skills/stryker-js in your project.
What does Stryker JS need to run?
Going by SKILL.md and its folder, Stryker JS needs JavaScript and TypeScript for the scripts in its folder and the command-line tools its instructions call (pnpm and just). Our summary lists: Node.js.
Does Stryker JS access the network?
SKILL.md names 2 domains. As links in the text: stryker-mutator.io and github.com. This is read from the text; nothing was executed.
Is Stryker JS 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 Stryker JS use?
No licence was found for Stryker JS or its repository. Without one, default copyright applies: ask the author before reusing or redistributing it.
How many tokens does Stryker JS use?
About 2.4k tokens (SKILL.md is roughly 9.8k 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 3.4k tokens, read only when the agent opens those files.
What are the alternatives to Stryker JS?
Skills that share tags, products or a category with Stryker JS: Check npm (grafana/skills, 281 stars), Apprun (yysun/apprun, 1.2k stars), E2E Test (crowdin/crowdin-api-client-js, 139 stars) and Supercov (supercorp-ai/supercov, 151 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Stryker JS?
mizchi (a GitHub user) maintains it in mizchi/skills, which has 359 GitHub stars. The repository holds 69 skills in this directory. The repository was last updated on October 2, 2026.
Source: mizchi/skills on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.