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 berkcangumusisik/claude-code-practices --skill test-mutationgit clone --depth 1 https://github.com/berkcangumusisik/claude-code-practicesWrote 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/berkcangumusisik/claude-code-practices/test-mutation)<a href="https://agentmods.dev/skills/berkcangumusisik/claude-code-practices/test-mutation"><img src="https://agentmods.dev/badge/skills/berkcangumusisik/claude-code-practices/test-mutation/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/berkcangumusisik/claude-code-practices/test-mutation"><img src="https://agentmods.dev/badge/skills/berkcangumusisik/claude-code-practices/test-mutation.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00016 | $0.00232 |
| Opus 5 | $0.00008 | $0.00116 |
| Sonnet 5 | $0.00003 | $0.00046 |
| Haiku 4.5 | $0.00002 | $0.00023 |
Grade A, and why
test-mutation 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 7d 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
Mutation Testing Analysis
Target: $1
Since we can't run Stryker/mutmut directly, do a manual mutation analysis:
-
Read the source file and its test file.
-
Apply common mutations mentally and check if existing tests would catch them:
- Change
>to>=(boundary condition) - Negate boolean conditions (
!) - Remove a function call
- Change
&&to|| - Return early / return null instead of computed value
- Off-by-one in loops
- Change
-
For each mutation that would NOT be caught:
- Describe the mutation
- Explain why it would go undetected
- Write a test that catches it
-
Report:
Surviving mutations found: N
Tests added: N
Estimated mutation score: X% → Y%
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.
- 7d ago First seen · 37 lines · 16 tokens per session scan A 2ddf2876071a
test-mutation is a skill published in the GitHub repository berkcangumusisik/claude-code-practices (10 stars, last pushed 4mo ago), licensed MIT. It adds 16 tokens to every session and 232 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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