Borrowing it
Nothing to install: this file belongs to Claritune/mutantx. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/Claritune/mutantx/main/CLAUDE.mdgit clone --depth 1 https://github.com/Claritune/mutantxWrote 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/instructions/claritune/mutantx/claude-md)<a href="https://agentmods.dev/instructions/claritune/mutantx/claude-md"><img src="https://agentmods.dev/badge/instructions/claritune/mutantx/claude-md/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/instructions/claritune/mutantx/claude-md"><img src="https://agentmods.dev/badge/instructions/claritune/mutantx/claude-md.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 | $0.00628 | $0.00628 |
| Opus 5.5 | $0.00251 | $0.00251 |
| Sonnet 5.5 | $0.00126 | $0.00126 |
| Haiku 4.5 | $0.00063 | $0.00063 |
Grade A, and why
mutantx CLAUDE.md 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 2mo 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.
How it starts
The opening of the file, as written. The whole thing — 79 lines — stays where its author put it; the contents beside it link to each section on GitHub.
MutantX
AI-powered mutation testing for Claude Code. Language-agnostic.
Workflow
Commit after each change. Do not batch multiple changes into one commit.
Project Structure
src/skills/ — Distributable Claude Code skills
src/scripts/ — Deterministic Python scripts (zero tokens)
src/agents/ — Distributable Claude Code agents
demos/python/ — Python demo project with intentional test gaps
demos/cpp/ — C++ demo project with intentional test gaps
Architecture
Phases 1-2 (detect, generate) use AI. Phases 3-4 (test, report) are deterministic Python scripts that consume zero tokens. Once mutants are generated, repeated testing is free.
| Phase | Component | AI? |
|---|---|---|
| Detect | /mx-detect skill |
Yes |
| Generate | /mx-generate skill |
Yes |
| Validate | mx-validate.py + /mx-validate skill |
Deterministic + optional AI |
| Test | mx-test.py script |
No |
| Report | mx-report.py script + /mx-report skill |
Partial |
Validation runs automatically before testing. If source files changed since generation, mutants are classified as valid, stale, or needs-review. The AI skill reviews ambiguous cases only.
Skills
| Skill | Purpose |
|---|---|
/mutate |
Full mutation testing run (orchestrates all phases) |
/mx-detect |
Phase 1: detect project language, test command, source files |
/mx-generate |
Phase 2: generate mutant patches with per-file caching |
/mx-validate |
Review mutants flagged as needs-review after file changes |
/mx-test |
Phase 3: invokes mx-test.py |
/mx-report |
Phase 4: invokes mx-report.py then adds AI analysis |
Agent
mx-agent runs the full mutation testing cycle autonomously without user interaction.
Installing for use
# Skills
cp -r src/skills/* ~/.claude/skills/
# Scripts (required for testing and reporting)
mkdir -p ~/.claude/scripts
cp src/scripts/*.py ~/.claude/scripts/
# Agent (optional)
mkdir -p ~/.claude/agents
cp src/agents/mx-agent.md ~/.claude/agents/
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.
- 2mo ago First seen · 79 lines · 628 tokens per session scan A a8c17a3504d9
mutantx CLAUDE.md is an instructions file published in the GitHub repository Claritune/mutantx (2 stars, last pushed yesterday), licensed MIT. It adds 628 tokens to every session, about $0.0025 per session on Opus 5.5. 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 2026-08-31.
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