mutation-test

mutation-test is a skill for Claude Code, Codex from nwiizo/ccswarm. It costs 25 tokens per session (194 once invoked), scanned A, original, MIT.

A test-quality check for Rust projects that changes code in small ways and sees whether the existing tests detect those changes. These changes are called mutants.

In plain words
What is it for?
Use it to run mutation tests on a Rust crate and review which changes were caught, missed, or took too long.
Why use it?
Passing tests do not always prove that tests would catch real bugs; missed mutants show where test coverage may be weak.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/nwiizo/ccswarm/mutation-test
Any agent
npx skills add nwiizo/ccswarm --skill mutation-test
Clone the repo
git clone --depth 1 https://github.com/nwiizo/ccswarm

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 mutation-test

README.md
[![agentmods](https://agentmods.dev/badge/skills/nwiizo/ccswarm/mutation-test.svg)](https://agentmods.dev/skills/nwiizo/ccswarm/mutation-test)
Your own site
<a href="https://agentmods.dev/skills/nwiizo/ccswarm/mutation-test"><img src="https://agentmods.dev/badge/skills/nwiizo/ccswarm/mutation-test.svg" alt="Measured on agentmods" height="20"></a>
Per session 25 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 194 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00025 $0.00194
Opus 5 $0.00013 $0.00097
Sonnet 5 $0.00005 $0.00039
Haiku 4.5 $0.00003 $0.00019

Measured 5d ago against content hash 86b6b4c8f624, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

mutation-test 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.

.agents/skills/mutation-test/SKILL.md · 27 lines

What it actually says

Run mutation tests on the specified crate (default: ccswarm):

# Install if needed
cargo mutants --version || cargo install cargo-mutants

# List mutants
cargo mutants --list -p $ARGUMENTS | head -50

# Run mutation tests
cargo mutants -p ${1:-ccswarm} --timeout 120 -j 4

# Report results
echo "=== Caught ===" && wc -l mutants.out/caught.txt
echo "=== Missed ===" && cat mutants.out/missed.txt
echo "=== Timeout ===" && wc -l mutants.out/timeout.txt

Focus on missed mutants in business logic - these indicate insufficient test coverage.

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 · 27 lines · 25 tokens per session scan A 86b6b4c8f624

Subscribe to this mod's changes

mutation-test is a skill published in the GitHub repository nwiizo/ccswarm (149 stars, last pushed 1mo ago), licensed MIT. It adds 25 tokens to every session and 194 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 2026-08-30.