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.
npx skills add codebygarv/Ai-skills --skill mutation-testing-advisorgit clone --depth 1 https://github.com/codebygarv/Ai-skillsWrote 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.
[](https://agentmods.dev/skills/codebygarv/ai-skills/mutation-testing-advisor)<a href="https://agentmods.dev/skills/codebygarv/ai-skills/mutation-testing-advisor"><img src="https://agentmods.dev/badge/skills/codebygarv/ai-skills/mutation-testing-advisor.svg" alt="Measured on agentmods" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00024 | $0.00357 |
| Opus 5 | $0.00012 | $0.00179 |
| Sonnet 5 | $0.00005 | $0.00071 |
| Haiku 4.5 | $0.00002 | $0.00036 |
Grade A, and why
mutation-testing-advisor 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.
What it actually says
Purpose
Evaluate the true fault-detection capability of a test suite by simulating code mutations (inverting conditionals, altering arithmetic, removing function calls) and highlighting tests that pass despite broken logic.
When to Use
- A codebase has 90%+ line coverage but bugs still regularly slip into production.
- Reviewing unit tests that assert on execution without verifying state changes.
- Setting up Stryker or Mutmut mutation testing in critical packages.
What to Analyze
- Mutant Categories:
- Conditional Boundary Mutations (
>swapped for>=). - Inverted Logic (
if (isValid)swapped forif (!isValid)). - Return Value Mutations (returning
nullorundefined). - Statement Deletions (removing side-effect calls).
- Conditional Boundary Mutations (
- Surviving Mutants: Why didn't any test fail when this line was corrupted?
- Weak Assertion Diagnosis: Identifying tests with no
expect()or vague assertions (e.g.expect(res).toBeDefined()). - Targeted Assertion Improvements: Writing specific assertions that kill surviving mutants.
Output Format
- Mutation Score Assessment: High-risk areas of false test confidence.
- Surviving Mutant Table: [File | Mutation | Why Test Passed | Fix].
- Hardened Test Code: Rewritten unit tests with strict state and error assertions.
Avoid
- Chasing 100% line coverage while leaving assertions superficial.
- Testing mock implementation details instead of real behavior.
What ships with it
2 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.
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.
- 5d ago First seen · 37 lines · 24 tokens per session scan A 7f37a4a63841
mutation-testing-advisor is a skill published in the GitHub repository codebygarv/Ai-skills (25 stars, last pushed 19d ago), licensed MIT. It adds 24 tokens to every session and 357 once invoked, about $0.0001 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.
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