Use the open-source free `Stryker.NET` mutation testing tool for .NET.
SkillScore68Maintained
Automatic
◆QA & Test Engineering pack
Last verified 8/19/2026
What it changes
Passed 12 of 17 test cases with the skill, and 7 of 17 without it.
Without skill41%
With skill68%
Checks it passed that the model alone missed
Output contains the field remaining.
Output reports status as not_applicable.
Output contains the field validation_skills.
and 7 more in the full report
8 fixed7 passed either way5 still failing2 broke
Pass-rate lift
+27 pp
Tokens
+11%
Agent turns
0%
Response time
-37%
Model gemini-3.6-flashMeasured 8/19/2026v115 of 22 cases passed with skill · 17 comparable
Tokens, turns and time describe resource use, not a dollar price.
See it in action
One of 8 test cases the skill fixed. Same model, same prompt, with and without the skill.
1 of 8
Prompt
Our team wants to assess mutation testing for our repository, but leadership decided that mutation testing is explicitly out of scope for our team's current quarterly milestones due to budget constraints. Please document this decision in our report format.
What was checked, without and with the skill
Checked
Without skill
With skill
Output reports status as not_applicable.
Missed
Passed
Output provides an explicit fallback path or rationale for excluding mutation testing.
Passed
Passed
case-06 · gemini-3.6-flash · 8/19/2026 · answers are capped and redacted
What's inside
The instructions your model reads when the skill loads.
SKILL.md100 lines4 files
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
Read the nearest AGENTS.md and confirm scope and constraints.
Run this skill's Workflow through the Ralph Loop until outcomes are acceptable.
Return the Required Result Format with concrete artifacts and verification evidence.
Workflow
Run mutation testing on critical projects, not blindly on the whole mono-repo.
Keep it out of the fastest PR path unless the repo explicitly accepts the runtime cost.
Stabilize tests first; mutation testing amplifies flaky or slow suites.
Provides guidance on new System.Text.Json APIs introduced in .NET 11. It covers typed JsonTypeInfo access via GetTypeInfo<T> and TryGetTypeInfo<T> on JsonSerializerOptions, and the new JsonNamingPolicy.PascalCase static property. Use when serializing or deserializing JSON in .NET 11 applications and needing typed metadata access or PascalCase property naming.