# Ruzzy

Sets up and runs Ruzzy, Trail of Bits' coverage-guided Ruby fuzzer and the only...

- Repository: https://github.com/trailofbits/skills (7935 stars)
- Category: Testing
- License: CC-BY-SA-4.0
- Last updated: 2026-10-28
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add trailofbits/skills --skill ruzzy -g -a claude-code -y`
Codex: `npx skills add trailofbits/skills --skill ruzzy -g -a codex -y`
Cursor: `npx skills add trailofbits/skills --skill ruzzy -g -a cursor -y`
Gemini CLI: `npx skills add trailofbits/skills --skill ruzzy -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add trailofbits/skills`

## Description

Sets up and runs Ruzzy, Trail of Bits' coverage-guided Ruby fuzzer and the only production-ready one for the language. Covers harness structure, fuzzing pure Ruby and the native C extensions in gems, and sanitizer builds. Use when fuzzing a Ruby library or gem, testing a Ruby C extension for memory safety, or asking how to fuzz Ruby at all.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Ruzzy

Ruzzy is a coverage-guided fuzzer for Ruby built on libFuzzer. It enables fuzzing both pure Ruby code and Ruby C extensions with sanitizer support for detecting memory corruption and undefined behavior.

## When to Use

Ruzzy is currently the only production-ready coverage-guided fuzzer for Ruby.

**Choose Ruzzy when:**
- Fuzzing Ruby applications or libraries
- Testing Ruby C extensions for memory safety issues
- You need coverage-guided fuzzing for Ruby code
- Working with Ruby gems that have native extensions

## Quick Start

Set up environment:
```bash
export ASAN_OPTIONS="allocator_may_return_null=1:detect_leaks=0:use_sigaltstack=0"
```

Test with the included toy example:
```bash
LD_PRELOAD=$(ruby -e 'require "ruzzy"; print Ruzzy::ASAN_PATH') \
    ruby -e 'require "ruzzy"; Ruzzy.dummy'
```

This should quickly find a crash demonstrating that Ruzzy is working correctly.

## Installation

### Platform Support

Ruzzy supports Linux x86-64 and AArch64/ARM64. For macOS or Windows, use the [Dockerfile](https://github.com/trailofbits/ruzzy/blob/main/Dockerfile) or [development environment](https://github.com/trailofbits/ruzzy#developing).

### Prerequisites

- Linux x86-64 or AArch64/ARM64
- Recent version of clang (tested back to 14.0.0, latest release recommended)
- Ruby with gem installed

### Installation Command

Install Ruzzy with clang compiler flags:

```bash
MAKE="make --environment-overrides V=1" \
CC="/path/to/clang" \
CXX="/path/to/clang++" \
LDSHARED="/path/to/clang -shared" \
LDSHAREDXX="/path/to/clang++ -shared" \
    gem install ruzzy
```

**Environment variables explained:**
- `MAKE`: Overrides make to respect subsequent environment variables
- `CC`, `CXX`, `LDSHARED`, `LDSHAREDXX`: Ensure proper clang binaries are used for latest features

### Troubleshooting Installation

If installation fails, enable debug output:

```bash
RUZZY_DEBUG=1 gem install --verbose ruzzy
```

### Verification

The rest: https://github.com/trailofbits/skills/blob/HEAD/plugins/testing-handbook-skills/skills/ruzzy/SKILL.md