Agent skill · Trail of Bits

Property-Based Testing skill for Claude Code, Codex and Cursor

Writes and debugs property-based tests with Hypothesis, fast-check, proptest and similar tools.

Officialname: property-based-testing★ 7.8k (repo)pushed 2026-10-24CC-BY-SA-4.0SKILL.md on GitHubchecked 2026-11-07

What it does, in the publisher's words

Writes, reviews, and debugs property-based tests — Hypothesis, fast-check, proptest, jqwik, rapid, and Echidna or Medusa for Solidity invariants.

The description field of the SKILL.md. The agent reads only this at startup and decides from it when to load the full skill.

Install Property-Based Testing

The skills CLI copies the skill into the folder of each agent you pick (Claude Code, Codex, Cursor, Copilot, Gemini CLI, OpenCode, Windsurf...). Add -g for all projects. Needs Node.js 22.20+. docs

npx skills add trailofbits/skills --skill property-based-testing

This repo is a plugin marketplace. Inside Claude Code, add it and install the plugin that holds the skill (audit-context-building, building-secure-contracts, burpsuite-project-parser, chrome-mcp-troubleshooting...), or copy only this skill into ~/.claude/skills. docs

/plugin marketplace add trailofbits/skills
/plugin install <plugin>@trailofbits

# or only this skill:
npx skills add trailofbits/skills --skill property-based-testing -a claude-code

Download the skill folder, zip it, then Customize > Skills > + > Create skill > Upload a skill. Code execution must be on (Settings > Capabilities). docs

git clone --depth 1 https://github.com/trailofbits/skills.git /tmp/property-based-testing-src
cp -r /tmp/property-based-testing-src/plugins/property-based-testing/skills/property-based-testing ./property-based-testing
zip -r property-based-testing.zip property-based-testing

Codex reads skills from .agents/skills in the repo or ~/.agents/skills. Type $ in Codex to use one. docs

npx skills add trailofbits/skills --skill property-based-testing -a codex

gh skill (GitHub CLI 2.90+, preview) installs it for Copilot in VS Code, the CLI and the cloud agent. Copilot also reads .github/skills and ~/.copilot/skills. docs

gh skill install trailofbits/skills property-based-testing

Cursor reads .cursor/skills, .agents/skills and ~/.cursor/skills (and .claude/skills). It does not install loose skills from a GitHub URL, so copy it in. docs

npx skills add trailofbits/skills --skill property-based-testing -a cursor

Installs from the GitHub repo; --path picks this skill out of the repo. Default scope is user (all projects). docs

gemini skills install https://github.com/trailofbits/skills.git --path plugins/property-based-testing/skills/property-based-testing

OpenCode reads .opencode/skills, ~/.config/opencode/skills and the Claude and .agents folders. docs

npx skills add trailofbits/skills --skill property-based-testing -a opencode

Windsurf (now Devin Desktop) reads .devin/skills, .windsurf/skills and ~/.codeium/windsurf/skills. docs

npx skills add trailofbits/skills --skill property-based-testing -a windsurf

Works with

Claude Code, Claude.ai and Claude Desktop, Codex, GitHub Copilot, Cursor, Gemini CLI, OpenCode, Windsurf and other agents that read the open Agent Skills format.

Uses effort in its frontmatter: Claude Code extensions to the Agent Skills format. Other agents load the skill but may not honor that field.

What's in the SKILL.md

4 sections

Property catalog
The two ways a property test asserts nothing
Where to look next
Introducing PBT to a project that lacks it

Bundled files

README.md
agents/openai.yaml
assets/trail-of-bits-mark.svg
references/generating.md
references/interpreting-failures.md
references/libraries.md
references/refactoring.md
references/reviewing.md

Loaded only when the instructions point to them.

Facts

Skill name: property-based-testing
Publisher: Trail of Bits (official)
Repo: trailofbits/skills
License: CC-BY-SA-4.0
SKILL.md size: 522 words, 63 lines
Bundled files: 8, 6 docs
Repo stars: 7.8k (as of 2026-10-24)
SKILL.md checked: 2026-11-07

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FAQ

What does the property-based-testing skill do?+

Writes and debugs property-based tests with Hypothesis, fast-check, proptest and similar tools. In its own SKILL.md, Trail of Bits describes it as: "Writes, reviews, and debugs property-based tests — Hypothesis, fast-check, proptest, jqwik, rapid, and Echidna or Medusa for Solidity invariants."

How do I install the property-based-testing skill?+

Run npx skills add trailofbits/skills --skill property-based-testing and pick your agents, or use the tab for your agent above. In Claude Code the skill ends up in ~/.claude/skills/property-based-testing/SKILL.md; in Codex and Cursor in .agents/skills/property-based-testing/.

Does Property-Based Testing work in Codex, Cursor and Copilot, or only Claude?+

It's a standard SKILL.md, so any agent that reads the Agent Skills format can use it: Claude Code, the Claude apps, Codex, GitHub Copilot, Cursor, Gemini CLI, OpenCode, Windsurf and more. It also sets effort, which are Claude Code extensions; other agents may ignore it.

Who maintains Property-Based Testing?+

Trail of Bits, the company or project behind it, in the trailofbits/skills repo on GitHub, last pushed 2026-10-24. License: CC-BY-SA-4.0.

Read a skill's SKILL.md and scripts before you install it: skills aren't verified by any agent vendor. Claude skills marketplace · How to install skills · MCP servers