A coverage-guided fuzzer for Ruby code and Ruby C extensions. Fuzzing automatically tries many inputs to find crashes, memory errors, and other unexpected behavior.

Use it to fuzz Ruby libraries, applications, gems with native extensions, or pure Ruby code. It supports Linux on x86-64 and ARM64, with Docker-based options for other systems.

It can uncover problems that hand-written tests may miss, including memory-safety issues in native Ruby extensions.

ruzzy — Skill for Claude Code by RedHatProductSecurity

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.

Any agent

npx skills add RedHatProductSecurity/prodsec-skills --skill ruzzy

Clone the repo

git clone --depth 1 https://github.com/RedHatProductSecurity/prodsec-skills

Made for: Claude Code.

Or install prodsec-skills, the plugin that ships this one along with the rest of its 133 skills.

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/redhatproductsecurity/prodsec-skills/ruzzy/github.svg)](https://agentmods.dev/skills/redhatproductsecurity/prodsec-skills/ruzzy)

Your own site

<a href="https://agentmods.dev/skills/redhatproductsecurity/prodsec-skills/ruzzy"><img src="https://agentmods.dev/badge/skills/redhatproductsecurity/prodsec-skills/ruzzy/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/redhatproductsecurity/prodsec-skills/ruzzy"><img src="https://agentmods.dev/badge/skills/redhatproductsecurity/prodsec-skills/ruzzy.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 30 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 3,193 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

Origin original 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.

Model	Per session	Once invoked
Fable 5.1	$0.00030	$0.03193
Opus 5	$0.00015	$0.01597
Sonnet 5	$0.00006	$0.00639
Haiku 4.5	$0.00003	$0.00319

Measured 9d ago against content hash da1c65ff09bb, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

ruzzy 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 9d 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

ruzzy — 98% identical, 7 lines differ

module/skills/ruzzy/SKILL.md · 447 lines

How it starts

The opening of the file, as written. The whole thing — 447 lines — stays where its author put it; the contents beside it link to each section on GitHub.

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:

export ASAN_OPTIONS="allocator_may_return_null=1:detect_leaks=0:use_sigaltstack=0"

Test with the included toy example:

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 installed and detecting bugs.

Installation

Platform Support

Ruzzy supports Linux x86-64 and AArch64/ARM64. For macOS or Windows, use the Dockerfile or development environment.

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:

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:

RUZZY_DEBUG=1 gem install --verbose ruzzy

Verification

Verify installation by running the toy example (see Quick Start section).

Read the full file on GitHub · 447 lines

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.

9d ago First seen · 447 lines · 30 tokens per session scan A da1c65ff09bb

Subscribe to this mod's changes

ruzzy is a skill published in the GitHub repository RedHatProductSecurity/prodsec-skills (52 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 30 tokens to every session and 3,193 once invoked, about $0.0002 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 2026-09-03.

Security Testing security_testing

research-engineer

An uncompromising Academic Research Engineer. Operates with absolute scientific rigor, objective criticism, and zero flair. Focuses on theoretical correctness, formal verification, and optimal implementation across any required technology.

davila7/claude-code-templates · 43 tokens

tika-eval-compare

Compare extracts from two Tika builds over a corpus to detect regressions in content, encoding, exceptions, and embedded-document handling. Use for "compare before/after extracts", "eval this change against the corpus".

apache/tika · 50 tokens

neuron-evaluation-engineer

Create and run AI evaluations with datasets, assertions, and output drivers in Neuron AI. Use this skill whenever the user mentions evaluation, testing AI systems, creating evaluators, dataset-driven testing, assertion-based validation, or wants to measure AI system performance. Also trigger for tasks involving…

neuron-core/neuron-ai · 77 tokens

ruzzy