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Agent skill

Stryker

by managedcode in managedcode/dotnet-skills

Use the open-source free Stryker.NET mutation testing tool for .NET.

MITAuto-check passedTesting & QA

Install Stryker

skills CLI
$ npx skills add managedcode/dotnet-skills --skill stryker -a claude-code

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

GitHub CLI
$ gh skill install managedcode/dotnet-skills stryker --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/managedcode/dotnet-skills.git skills-src && mkdir -p .claude/skills && cp -r skills-src/catalog/Testing/Stryker/skills/stryker .claude/skills/stryker && 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/

Facts

Skill name
stryker
GitHub stars
486
Token cost
~1k tokens
SKILL.md length
479 words
Files
5 (incl. references)
Skills in repo
81
Repo updated
First seen
Licence
MIT

At a glance

Use the open-source free Stryker.NET mutation testing tool for .NET.

  • Works in 3 steps: Read the nearest AGENTS.md and confirm… → Run this skill's Workflow through the… → Return the Required Result Format with…
  • A repo needs to measure whether tests actually catch faults
  • SKILL.md covers Trigger On, Value, Do Not Use For and Inputs, plus 8 more sections
  • Calls dotnet and rg

What it does

Stryker is an agent skill from managedcode/dotnet-skills. Use the open-source free Stryker.NET mutation testing tool for .NET. Use when a repo needs to measure whether tests actually catch faults, especially in critical libraries or domains. USE FOR: the repo uses or wants Stryker.NET; mutation testing is needed for high-risk code. DO NOT USE FOR: every PR path by default in a large repo; simple coverage collection. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.

Its SKILL.md is about 1k tokens, which your agent loads only when the skill is triggered. The skill folder holds 5 other files, including reference files (for example `manifest.json`, `references/commands.md` and `references/patterns.md`). Compatibility notes: Requires a .NET test project or solution; respects the repo's AGENTS.md commands first.

It sits in Testing & QA, covering Test coverage and Codebase knowledge for agents. It works with .NET. The repository describes itself as: Installable .NET skill catalog and CLI for Codex, Claude Code, GitHub Copilot, and Gemini. The licence is MIT.

When your agent uses it

  • A repo needs to measure whether tests actually catch faults
  • Especially in critical libraries
  • : the repo uses
  • Wants Stryker.NET

Example prompts

  • “/stryker”

Requirements

  • Compatibility (from SKILL.md): Requires a .NET test project or solution; respects the repo's `AGENTS.md` commands first.

Workflow steps

3 steps, taken from the first numbered list in SKILL.md.

  1. Read the nearest AGENTS.md and confirm scope and constraints.
  2. Run this skill's Workflow through the Ralph Loop until outcomes are acceptable.
  3. Return the Required Result Format with concrete artifacts and verification evidence.

What it can do on your machine

Read from SKILL.md and the folder at commit 535dd55. 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:

    • dotnet
    • rg

    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.

  • Compatibility

    Requires a .NET test project or solution; respects the repo's `AGENTS.md` commands first.

    From compatibility in the SKILL.md frontmatter.

Context cost

Stryker loads about 1k tokens when it runs, and up to ~3.9k if it reads all its reference files. Until then it costs about 129 tokens; SKILL.md has 479 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~129
When it runs · the whole SKILL.md, loaded when a task matches
~1k
With references · SKILL.md plus every file in references/, read only if the agent opens them
~3.9k

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 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 managedcode/dotnet-skills at commit 535dd55, republished under its MIT licence (© managedcode). 479 words, ~1,047 tokens.

Download SKILL.mdSave it as .claude/skills/stryker/SKILL.md (or your agent's skills folder). This skill also uses 4 other files; get the full folder from GitHub.
name
stryker
description
Use the open-source free `Stryker.NET` mutation testing tool for .NET. Use when a repo needs to measure whether tests actually catch faults, especially in critical libraries or domains. USE FOR: the repo uses or wants Stryker.NET; mutation testing is needed for high-risk code. DO NOT USE FOR: every PR path by default in a large repo; simple coverage collection. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made.
compatibility
Requires a .NET test project or solution; respects the repo's `AGENTS.md` commands first.

Stryker.NET

Trigger On

  • the repo uses or wants Stryker.NET
  • mutation testing is needed for high-risk code

Value

  • produce a concrete project delta: code, docs, config, tests, CI, or review artifact
  • reduce ambiguity through explicit planning, verification, and final validation skills
  • leave reusable project context so future tasks are faster and safer

Do Not Use For

  • every PR path by default in a large repo
  • simple coverage collection

Inputs

  • the nearest AGENTS.md
  • target projects and critical paths
  • time budget for mutation runs

Quick Start

  1. Read the nearest AGENTS.md and confirm scope and constraints.
  2. Run this skill's Workflow through the Ralph Loop until outcomes are acceptable.
  3. Return the Required Result Format with concrete artifacts and verification evidence.

Workflow

  1. Run mutation testing on critical projects, not blindly on the whole mono-repo.
  2. Keep it out of the fastest PR path unless the repo explicitly accepts the runtime cost.
  3. Stabilize tests first; mutation testing amplifies flaky or slow suites.

Bootstrap When Missing

If Stryker.NET is not configured yet:

  1. Detect current state:
    • rg --files -g '.config/dotnet-tools.json'
    • dotnet tool list --local
    • dotnet tool list --global
  2. Prefer local tool installation for reproducible CI:
    • dotnet new tool-manifest (if missing)
    • dotnet tool install stryker
  3. Choose a focused target scope and mutation budget before enabling CI.
  4. Add a dedicated mutation command in AGENTS.md and CI (not in the fastest PR path by default).
  5. Run dotnet stryker on the target project and return status: configured or status: improved.
  6. If mutation testing is explicitly out of scope, return status: not_applicable.

Deliver

  • explicit mutation-test scope
  • reproducible Stryker commands

Validate

  • the selected scope is affordable in CI
  • mutation score is interpreted with test quality, not as a vanity number
Show full SKILL.md (193 more words)Show less

Ralph Loop

Use the Ralph Loop for every task, including docs, architecture, testing, and tooling work.

  1. Plan first (mandatory):
    • analyze current state
    • define target outcome, constraints, and risks
    • write a detailed execution plan
    • list final validation skills to run at the end, with order and reason
  2. Execute one planned step and produce a concrete delta.
  3. Review the result and capture findings with actionable next fixes.
  4. Apply fixes in small batches and rerun the relevant checks or review steps.
  5. Update the plan after each iteration.
  6. Repeat until outcomes are acceptable or only explicit exceptions remain.
  7. If a dependency is missing, bootstrap it or return status: not_applicable with explicit reason and fallback path.
Required Result Format
  • status: complete | clean | improved | configured | not_applicable | blocked
  • plan: concise plan and current iteration step
  • actions_taken: concrete changes made
  • validation_skills: final skills run, or skipped with reasons
  • verification: commands, checks, or review evidence summary
  • remaining: top unresolved items or none

For setup-only requests with no execution, return status: configured and exact next commands.

Load References

Example Requests

  • "Add Stryker for this library."
  • "Use mutation testing on our critical domain layer."

© managedcode, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 4 other files (references) in catalog/Testing/Stryker/skills/stryker of managedcode/dotnet-skills.

  • SKILL.md
  • manifest.json
  • references/commands.md
  • references/patterns.md
  • references/stryker.md

Open the folder on GitHubat commit 535dd55

Compare with similar skills

Stryker 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.

Stryker compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Stryker this skillmanagedcode/dotnet-skills486—~1kAutomated safety check: PassMIT
Mcaf Dotnet Quality CImanagedcode/Storage138—~1.7kAutomated safety check: PassMIT
Mcaf Dotnet Strykermanagedcode/Storage138—~946Automated safety check: PassMIT
Evaluate PR Testsdotnet/maui23k—~2.9kAutomated safety check: PassMIT
Find Untested Sourcesdotnet/skills5.6k1 repos~3.3kAutomated safety check: PassMIT
Coverage Analysismicrosoft/testfx1k—~7.3kAutomated safety check: PassMIT

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  • Mcaf Dotnet Stryker

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Works with

Categories

Questions about Stryker

What does Stryker do?

Use the open-source free Stryker.NET mutation testing tool for .NET. Stryker is an agent skill from managedcode/dotnet-skills.NET.

When should I use Stryker?

Stryker fits situations like: A repo needs to measure whether tests actually catch faults; especially in critical libraries; : the repo uses; wants Stryker.NET.

How do I install Stryker in Claude Code?

Run `npx skills add managedcode/dotnet-skills --skill stryker -a claude-code`. Or copy the skill folder (catalog/Testing/Stryker/skills/stryker in managedcode/dotnet-skills) into .claude/skills/stryker in your project. Claude Code loads it when a task matches its description.

How do I install Stryker in Codex?

Run `npx skills add managedcode/dotnet-skills --skill stryker -a codex`. Or copy the skill folder (catalog/Testing/Stryker/skills/stryker in managedcode/dotnet-skills) into .agents/skills/stryker in your project. Codex loads it when a task matches its description.

Can I use Stryker 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 managedcode/dotnet-skills --skill stryker -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, .gemini/skills/stryker, .github/skills/stryker and .opencode/skills/stryker in your project.

What does Stryker need to run?

Going by SKILL.md and its folder, Stryker needs the command-line tools its instructions call (dotnet and rg). Compatibility (from SKILL.md): Requires a .NET test project or solution; respects the repo's `AGENTS.md` commands first..

Does Stryker 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 Stryker 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 use?

Stryker 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 Stryker use?

About 1k tokens (SKILL.md is roughly 4.2k 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 2.9k tokens, read only when the agent opens those files.

What are the alternatives to Stryker?

Skills that share tags, products or a category with Stryker: Mcaf Dotnet Quality CI (managedcode/Storage, 138 stars), Mcaf Dotnet Stryker (managedcode/Storage, 138 stars), Evaluate PR Tests (dotnet/maui, 23k stars) and Find Untested Sources (dotnet/skills, 5.6k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Stryker?

managedcode (a GitHub organization) maintains it in managedcode/dotnet-skills, which has 486 GitHub stars. The repository holds 81 skills in this directory. The repository was last updated on October 7, 2026.

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