# Property Based Testing (agent skill)

> Property Based Testing is an agent skill (a SKILL.md file) from trailofbits/skills. Writes, reviews, and debugs property-based tests — Hypothesis, fast-check, proptest, jqwik, rapid, and Echidna or Medusa for Solidity invariants. It works with Claude Code and Codex and has 7,804 GitHub stars across a repository of 4 listed skills.

Writes, reviews, and debugs property-based tests — Hypothesis, fast-check, proptest, jqwik, rapid, and Echidna or Medusa for Solidity invariants. Use whenever tests should cover a whole input domain instead of a hand-picked list of examples: encode/decode and serialize/deserialize pairs, parsers, canonicalizers and normalizers, validators, numeric and Decimal types, comparators and sort order, data structures, and smart-contract state invariants.

## Key facts

| Fact | Value |
|---|---|
| Repository | https://github.com/trailofbits/skills |
| Skill path | plugins/property-based-testing/skills/property-based-testing/SKILL.md |
| Skill name | property-based-testing |
| GitHub stars | 7,804 |
| Installs on skills.sh | 2 |
| License | CC-BY-SA-4.0 |
| Skills in repo | 4 |
| Plugin marketplace | trailofbits |
| Official | yes |
| Works with | Claude Code, Codex |
| Category | Testing & QA |
| Last commit | Oct 23, 2026 |

## When it triggers

- use when adding cases to an existing @given, fast-check, or proptest suite, when judging whether existing property tests assert anything real, and when a generator has shrunk a counterexample and you need to tell a wrong property from a gen

## Add this skill

### Claude Code

```sh
/plugin marketplace add trailofbits/skills
/plugin install property-based-testing@trailofbits
```

In the Claude apps, zip the skill folder and upload it under Customize > Skills > + > Upload a skill (code execution must be on).

### ChatGPT / Codex

```sh
git clone --depth 1 https://github.com/trailofbits/skills.git
cp -r skills/plugins/property-based-testing/skills/property-based-testing .agents/skills/property-based-testing   # repo; ~/.agents/skills for all projects
```

### Cursor

```sh
git clone --depth 1 https://github.com/trailofbits/skills.git
cp -r skills/plugins/property-based-testing/skills/property-based-testing .cursor/skills/property-based-testing   # project; ~/.cursor/skills for all projects
```

Sources (checked 2026-10-07): https://code.claude.com/docs/en/skills, https://support.claude.com/en/articles/12512180-using-skills-in-claude, https://learn.chatgpt.com/docs/build-skills, https://cursor.com/docs/context/skills

skills.sh listing: https://www.skills.sh/trailofbits/skills/property-based-testing

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Canonical page: https://appsgit.com/skills/trailofbits-property-based-testing
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