ruzzy

Overview of ruzzy skill

What ruzzy is for

The ruzy skill helps you use Ruzzy, a coverage-guided Ruby fuzzer built on libFuzzer. It is aimed at people who want to fuzz Ruby code, especially Ruby C extensions, with sanitizer-backed crash detection. If you need a ruzy install and usage path that is more concrete than a repo skim, this skill is for security testing work, not general Ruby automation.

Who should use it

Use the ruzzy skill if you are:

• testing a Ruby gem with native extensions
• looking for memory corruption or undefined behavior in Ruby C code
• validating parser, serializer, or input-handling paths with fuzzing
• deciding whether Ruzzy fits a Security Audit workflow

It is less useful if you only need unit tests, simple property tests, or black-box app testing without a native-code target.

What makes it different

Ruzzy is positioned as the production-ready option for coverage-guided fuzzing in Ruby. The practical difference is that it gives you feedback from code coverage and sanitizers, so it is better at finding hard failures than a generic “throw random inputs at it” prompt. The main tradeoff is setup cost: you need the right Ruby, clang, and Linux environment, and you need a target that can actually be fuzzed.

How to Use ruzzy skill

Install and verify the environment

For ruzy install, start from the skill and the repository’s SKILL.md. The repo says Ruzzy supports Linux x86-64 and AArch64/ARM64. For macOS or Windows, you need the Dockerfile or the development environment instead of a native install.

A practical installation check looks like this:

export ASAN_OPTIONS="allocator_may_return_null=1:detect_leaks=0:use_sigaltstack=0"
LD_PRELOAD=$(ruby -e 'require "ruzzy"; print Ruzzy::ASAN_PATH') \
  ruby -e 'require "ruzzy"; Ruzzy.dummy'

If that toy run crashes as expected, the build and sanitizer wiring are working.

Turn a rough goal into a usable prompt

For good ruzy usage, do not ask vaguely to “fuzz my gem.” Give the skill enough detail to choose an entry point and a harness. Include:

• target gem or repository name
• whether you are fuzzing pure Ruby or a C extension
• the method, parser, or API to drive
• sample input format
• whether crashes, hangs, or coverage growth matter most

Better input:

“Use ruzzy for Security Audit on this Ruby C extension. The target is MyGem::Parser.parse, which accepts a string payload and can reach native code. Help me build a minimal harness and a seed corpus for malformed JSON-like inputs.”

What to read first in the repo

Start with SKILL.md, then inspect the sections on:

• When to Use
• Quick Start
• Installation
• Platform Support

If you need to adapt the workflow, read the installation command and any inline repo references before copying examples into your own project. The biggest adoption blocker is usually platform mismatch or trying to fuzz the wrong abstraction level.

Workflow that works in practice

A solid ruzy guide flow is:

1. confirm platform and Ruby/clang prerequisites
2. verify the ASAN preload setup
3. choose one small, deterministic entry point
4. build a minimal harness around that entry point
5. run short fuzzing sessions first, then expand coverage

For Security Audit work, keep the initial scope narrow. One stable target with clear input boundaries is usually more valuable than fuzzing an entire app surface at once.

ruzzy skill FAQ

Is ruzzy only for native extensions?

No. The skill supports both pure Ruby code and Ruby C extensions, but it is most compelling when native code is in play. If your goal is only application logic testing, a normal test suite or property-based testing may be simpler.

Is ruzzy hard to install?

The ruzy install path is straightforward on supported Linux systems, but environment details matter. clang, Ruby, and sanitizer configuration must line up. If you are on macOS or Windows, expect to use Docker or a development environment instead of a direct native install.

When should I not use ruzzy?

Do not use Ruzzy when the target cannot be exercised repeatedly, when you cannot isolate a stable input entry point, or when the code depends heavily on external services. In those cases, the fuzzing signal will be weak and setup cost will outweigh value.

Is it suitable for beginners?

Yes, if you already know which function or parser you want to test. It is not the easiest first security tool if you still need to discover your target surface. Beginners get the best results when they start with the toy example and then adapt one small harness.

How to Improve ruzzy skill

Give the skill a narrower target

The biggest quality jump comes from narrowing the target. Instead of “fuzz my gem,” specify the exact callable surface, expected input type, and failure class you care about. For example, “find crashes in decode(input_string) caused by malformed UTF-8 and nested delimiters” is much better than a generic request.

Seed with real inputs and edge cases

Ruzzy gets better results when you provide representative seeds, especially if your target has structured input. Include:

• 3–10 valid examples
• malformed variants
• boundary cases like empty strings, huge buffers, and truncated data

This matters more than verbose instructions because the initial corpus shapes exploration.

Iterate on crashes, hangs, and coverage

After the first run, improve the harness before scaling runtime. If you see crashes, isolate the smallest reproducer. If you see hangs, tighten timeouts and simplify state. If coverage stalls, reduce setup overhead and remove unnecessary dependencies from the harness. That feedback loop is where ruzy usage becomes effective for Security Audit work.