stryker

stryker is a skill for Claude Code, Codex from managedcode/dotnet-skills. It costs 112 tokens per session (958 once invoked), scanned A, original, MIT.

A .NET mutation-testing tool that deliberately makes small changes to production code to check whether the test suite detects them.

In plain words
What is it for?
It is for measuring whether tests catch realistic faults in critical projects and deciding where additional tests are needed.
Why use it?
It reveals tests that may pass even when important code behaviour is broken, especially in high-risk areas.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions AGENTS.md.

Good fit It is for measuring whether tests catch realistic faults in critical projects and deciding where additional tests are needed.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/managedcode/dotnet-skills/stryker
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add managedcode/dotnet-skills --skill stryker
Clone the repo
git clone --depth 1 https://github.com/managedcode/dotnet-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for stryker

README.md
[![agentmods](https://agentmods.dev/badge/skills/managedcode/dotnet-skills/stryker.svg)](https://agentmods.dev/skills/managedcode/dotnet-skills/stryker)
Your own site
<a href="https://agentmods.dev/skills/managedcode/dotnet-skills/stryker"><img src="https://agentmods.dev/badge/skills/managedcode/dotnet-skills/stryker.svg" alt="Measured on agentmods" height="20"></a>
Per session 112 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 958 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00112 $0.00958
Opus 5 $0.00056 $0.00479
Sonnet 5 $0.00022 $0.00192
Haiku 4.5 $0.00011 $0.00096

Measured 5d ago against content hash b80587ad9e28, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

stryker scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

3 near-identical copies found in the catalogue:

catalog/Testing/Stryker/skills/stryker/SKILL.md · 107 lines

How it starts

The opening of the file, as written. The whole thing — 107 lines — stays where its author put it; the contents beside it link to each section on GitHub.

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

Read the full file on GitHub · 107 lines

Files

What ships with it

4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 5d ago First seen · 107 lines · 112 tokens per session scan A b80587ad9e28

Subscribe to this mod's changes

stryker is a skill published in the GitHub repository managedcode/dotnet-skills (477 stars, last pushed 3d ago), licensed MIT. It adds 112 tokens to every session and 958 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.