mutation-testing

mutation-testing is a skill for Claude Code from CraftOS-dev/CraftBot. It costs 53 tokens per session (685 once invoked), scanned A, original, MIT.

A configuration helper for mutation testing tools such as mewt and muton. Mutation testing changes code in controlled ways to check whether a test suite detects those changes.

In plain words
What is it for?
Use it to choose targets, set timeouts, and prepare mewt or muton campaigns for Rust, Solidity, Go, TypeScript, JavaScript, Java, or TON smart-contract languages.
Why use it?
It helps set up and tune long-running mutation-testing runs instead of configuring each campaign manually.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

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/craftos-dev/craftbot/mutation-testing
Any agent
npx skills add CraftOS-dev/CraftBot --skill mutation-testing
Clone the repo
git clone --depth 1 https://github.com/CraftOS-dev/CraftBot

Made for: Claude Code.

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-testing

README.md
[![agentmods](https://agentmods.dev/badge/skills/craftos-dev/craftbot/mutation-testing.svg)](https://agentmods.dev/skills/craftos-dev/craftbot/mutation-testing)
Your own site
<a href="https://agentmods.dev/skills/craftos-dev/craftbot/mutation-testing"><img src="https://agentmods.dev/badge/skills/craftos-dev/craftbot/mutation-testing.svg" alt="Measured on agentmods" height="20"></a>
Per session 53 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 685 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 5.1 $0.00053 $0.00685
Opus 5 $0.00026 $0.00342
Sonnet 5 $0.00011 $0.00137
Haiku 4.5 $0.00005 $0.00068

Measured 2d ago against content hash 1bb6b5ddaf79, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

mutation-testing 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 2d 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.

Origin

Copies of this mod

2 near-identical copies found in the catalogue:

skills/mutation-testing/SKILL.md · 73 lines

How it starts

The opening of the file, as written. The whole thing — 73 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Mutation Testing — Campaign Configuration (mewt/muton)

Note: muton and mewt share identical interfaces but target different languages — mewt for general-purpose languages (Rust, Solidity, Go, TypeScript, JavaScript), muton for TON smart contracts (Tact, Tolk, FunC). All examples use mewt commands, but they work exactly the same with muton. File names change accordingly: mewt.tomlmuton.toml, mewt.sqlitemuton.sqlite.

When to Use

Use this skill when the user:

  • Mentions "mewt", "muton", or "mutation testing"
  • Needs to configure or optimize a mutation testing campaign
  • Wants to run mewt run and needs help getting set up first

When NOT to Use

Do not use this skill when the user:

  • Wants to analyze or report on completed campaign results
  • Asks about tests or coverage without mentioning mutation testing

Quick Start

Load workflows/configuration.md — a 5-phase guide from mewt init to a validated, ready-to-run campaign.

General question or unfamiliar command? Run mewt --help or mewt <subcommand> --help, then assist.


Reference Index

File Content
workflows/configuration.md 5-phase guide: init, scope, optimize, validate, run
references/optimization-strategies.md Per-file targeting, two-phase campaigns, mutation type filtering

Essential Commands

# Initialize and mutate
mewt init                    # Create mewt.toml and mewt.sqlite
mewt mutate [paths]          # Generate mutants without running tests
mewt run [paths]             # Run the full campaign

# Inspect configuration and scope
mewt print config            # View effective configuration
mewt print targets           # Table of all targeted files
mewt print mutations --language [lang]  # Available mutation types
mewt status                  # Mutant count and per-file breakdown

# Investigate specific mutants
mewt print mutants --target [path]   # All mutants for a file
mewt print mutants --severity high   # Filter by severity
mewt print mutant --id [id]          # View mutated code diff
mewt test --ids [ids]                # Re-test specific mutants

Read the full file on GitHub · 73 lines

Files

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.

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. 2d ago First seen · 73 lines · 53 tokens per session scan A 1bb6b5ddaf79

Subscribe to this mod's changes

mutation-testing is a skill published in the GitHub repository CraftOS-dev/CraftBot (378 stars, last pushed 3d ago), licensed MIT. It adds 53 tokens to every session and 685 once invoked, about $0.0003 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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