A testing add-on that detects a project's technology stack, creates tests, measures code coverage, and uses mutation testing to check whether tests catch deliberately introduced mistakes.

It helps set up testing, add tests, measure coverage, and verify that tests can detect regressions and incorrect code.

It helps reveal when a project has too few tests or tests that pass without detecting real bugs. Code coverage shows what code tests run, while mutation testing checks whether those tests notice small changes.

fortify — Plugin by catcatcatstudio

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.

Claude Code

/plugin marketplace add catcatcatstudio/cat-skills

agentmods

npx agentmods add plugins/catcatcatstudio/cat-skills/fortify

Clone the repo

git clone --depth 1 https://github.com/catcatcatstudio/cat-skills

Made for: Claude Code.

Per session not measured What this adds to a session before it is invoked.

When invoked not measured Not applicable: nothing here is loaded into a session.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Security

Grade A, and why

fortify 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.

skills/fortify/.claude-plugin/plugin.json · 14 lines

What it actually says

{
  "name": "fortify",
  "description": "Testing infrastructure, coverage, and verified test quality — detects stack, writes tests, runs mutation testing",
  "version": "1.0.0",
  "author": {
    "name": "catcatcat",
    "url": "https://catcatcat.ai"
  },
  "homepage": "https://github.com/catcatcatstudio/cat-skills",
  "repository": "https://github.com/catcatcatstudio/cat-skills",
  "license": "MIT",
  "keywords": ["testing", "coverage", "mutation-testing", "quality", "infrastructure"]
}

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.

2d ago First seen · 14 lines scan A 11bb01dbf110

Subscribe to this mod's changes

fortify is a plugin published in the GitHub repository catcatcatstudio/cat-skills (3 stars, last pushed 5d ago), licensed MIT. Its token cost is not measured: this kind of file is read by the harness, not the model. 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.

Testing agent-skills ai-agent claude-code claude-code-plugin claude-code-skill claude-skills

fortify

Getting it into your agent

Grade A, and why

Nothing flagged

What it actually says

What this file has done since we first saw it

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