mutation-check

mutation-check is a skill for Claude Code, Codex from iansmith/slopstop. It costs 73 tokens per session (4,413 once invoked), scanned A, original, no licence file.

A test-checking workflow that determines whether a test fails for the behavior it claims to cover. It can also break that behavior deliberately to check whether an already passing test turns red.

In plain words
What is it for?
It is for checking newly written tests or backfilling existing ones, with a verdict for each test and an overall result such as PASS, FAIL, PINNED, or NOT PINNED.
Why use it?
It catches tests that pass or fail for unrelated reasons and therefore do not reliably protect the intended behavior.

Skill for Claude CodeCodex

Part of the slopstop plugin — 19 skills, 5 agents shipped together

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/iansmith/slopstop/mutation-check
Any agent
npx skills add iansmith/slopstop --skill mutation-check
Clone the repo
git clone --depth 1 https://github.com/iansmith/slopstop

Made for: Claude Code, Codex.

Or install slopstop, the plugin that ships this one along with the rest of its 19 skills, 5 agents.

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-check

README.md
[![agentmods](https://agentmods.dev/badge/skills/iansmith/slopstop/mutation-check.svg)](https://agentmods.dev/skills/iansmith/slopstop/mutation-check)
Your own site
<a href="https://agentmods.dev/skills/iansmith/slopstop/mutation-check"><img src="https://agentmods.dev/badge/skills/iansmith/slopstop/mutation-check.svg" alt="Measured on agentmods" height="20"></a>
Per session 73 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 4,413 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin unknown 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 $0.00073 $0.04413
Opus 5 $0.00036 $0.02207
Sonnet 5 $0.00015 $0.00883
Haiku 4.5 $0.00007 $0.00441

Measured 3d ago against content hash 5fe846577885, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

mutation-check 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 3d 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.

skills/mutation-check/SKILL.md · 310 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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. 3d ago First seen · 310 lines · 73 tokens per session scan A 5fe846577885

Subscribe to this mod's changes

mutation-check is a skill published in the GitHub repository iansmith/slopstop (2 stars, last pushed 4d ago), with no licence file. It adds 73 tokens to every session and 4,413 once invoked, about $0.0004 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 2026-08-31.

Related

Other skills, from other repositories

dev-kit-setup

First-use bootstrap for the dev kit. Detects the team's issue tracker, discovers what it can via MCP/CLI, asks only what cannot be discovered, and persists the result to .claude/dev-kit.json in the consuming repo. Use when that file is missing, when the user asks to set up or reconfigure the kit, or when issue-fetch…

theam/claude-dev-kit · 81 tokens

pr-review

Structured review of a pull request or the current diff - correctness, contract drift, security, missing tests, coverage gate - producing classified findings and a verdict. Use when the user asks to review a PR or diff, or as the self-review step of the story workflow.

theam/claude-dev-kit · 57 tokens

coverage-check

Run the repo's unit tests with coverage and verify that every file touched in the current change keeps line, branch, and function coverage at or above 95%. Language- and framework-agnostic. Use before committing, before PR creation, or when the user asks about coverage.

theam/claude-dev-kit · 59 tokens

create-pr

Create a branch, commit the work, and open a pull request for a completed user story, after all quality gates pass. Use when the user asks to open/create a PR or as the final step of the story workflow.

theam/claude-dev-kit · 48 tokens

fix-pr

Resolve the findings on an existing pull request - review comments, CI failures, and self-review findings - driving each to a decision (fix / defer to a tracked issue / discard), re-verifying the gates, replying to each reviewer, and watching for late feedback. The counterpart to pr-review that closes the loop.

theam/claude-dev-kit · 66 tokens

issue-fetch

Fetch a work item (summary, status, description, acceptance criteria, comments) from the team's issue tracker and display a clean summary. Supports Jira, Linear, GitHub Issues, and Azure DevOps via adapters. Use whenever a prompt contains an issue reference (e.g. PROJ-1234, ENG-42.

theam/claude-dev-kit · 68 tokens