libfuzzer

libfuzzer is a skill for Claude Code, Codex from OutlineDriven/odin-claude-plugin. It costs 45 tokens per session (3,789 once invoked), scanned A, original, Apache-2.0.

A tool for running and investigating coverage-guided fuzzing campaigns for C and C++ code with libFuzzer or AFL++. Fuzzing repeatedly feeds unusual or random inputs to software to find crashes and other failures.

In plain words
What is it for?
Use it to build or run a fuzzing campaign, tune it, or reproduce and investigate a crash found by the campaign.
Why use it?
It helps discover inputs that ordinary tests may miss and makes crash results reproducible. It also manages campaign output such as test cases, logs, and failure files.

Skill for Claude CodeCodex

Written for Claude Code and Codex: shipped in a Claude Code plugin, but also agents/openai.yaml present.

Part of the odin-fuzzing plugin — 12 skills shipped together

Good fit Use it to build or run a fuzzing campaign, tune it, or reproduce and investigate a crash found by the campaign.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/outlinedriven/odin-claude-plugin/libfuzzer
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 OutlineDriven/odin-claude-plugin --skill libfuzzer
Clone the repo
git clone --depth 1 https://github.com/OutlineDriven/odin-claude-plugin

Made for: Claude Code, Codex.

Or install odin-fuzzing, the plugin that ships this one along with the rest of its 12 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.

agentmods badge for libfuzzer

README.md
[![agentmods](https://agentmods.dev/badge/skills/outlinedriven/odin-claude-plugin/libfuzzer.svg)](https://agentmods.dev/skills/outlinedriven/odin-claude-plugin/libfuzzer)
Your own site
<a href="https://agentmods.dev/skills/outlinedriven/odin-claude-plugin/libfuzzer"><img src="https://agentmods.dev/badge/skills/outlinedriven/odin-claude-plugin/libfuzzer.svg" alt="Measured on agentmods" height="20"></a>
Per session 45 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,789 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 warn 7 Sept 2026
SkillSpector: 3 findings, up to medium

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • medium MCP Rug Pull · line 32
    Docker image references without a specific tag (:latest is implicit) or digest (@sha256:...) can be silently replaced by a malicious image.
    Fix: Pin the image: image:tag or image@sha256:abc123
  • medium MCP Rug Pull · line 32
    Docker image references without a specific tag (:latest is implicit) or digest (@sha256:...) can be silently replaced by a malicious image.
    Fix: Pin the image: image:tag or image@sha256:abc123
  • low Tool Misuse · line 32
    Tool parameters are crafted to achieve unintended or unsafe behavior. Parameter abuse can bypass intended safety checks (e.g. shell=True, --force, dangerous glob patterns).
    Fix: Validate all tool parameters against an allowlist. Reject dangerous parameter values (shell=True, --force, -rf /) and use safe defaults.
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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00045 $0.03789
Opus 5 $0.00023 $0.01895
Sonnet 5 $0.00009 $0.00758
Haiku 4.5 $0.00005 $0.00379

Measured 2d ago against content hash 1a63b067a964, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

libfuzzer 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 2d 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.

plugins/odin-fuzzing/skills/libfuzzer/SKILL.md · 133 lines

How it starts

The opening of the file, as written. The whole thing — 133 lines — stays where its author put it; the contents beside it link to each section on GitHub.

libFuzzer and AFL++

Contract

Field Bound contract
Trigger User needs to build, run, tune, or triage a coverage-guided C/C++ fuzzing campaign or LLVMFuzzerTestOneInput harness on the libFuzzer engine (default) or the AFL++ engine (afl mode).
Authority Human-gated: in afl mode, request explicit user approval before a package installation or a Docker image pull; otherwise reversible local: writes only named fuzzing artifacts (binary, corpus and output directories, crash files, logs); rollback is deleting them and killing campaign processes. Kernel-tuning steps that need a reboot or degrade OS security are out of scope. No remote mutation.
Side effect Local write to a compiled fuzzing binary, its corpus or output directory, log files, and any crash artifacts written by the target; afl mode may run a short-lived Docker container.
Done The instrumented binary runs against its corpus and any crash artifact reproduces in the same target with identical sanitizer output or signal.

Inputs

  • Required: Engine: libfuzzer (default) or afl.
  • Required: Source or object files for the code under test.
  • Required (libfuzzer engine): Clang compiler (clang++) with the libFuzzer runtime present, and one LLVMFuzzerTestOneInput harness function visible to the linker.
  • Required (afl engine): afl-fuzz on the host or the aflplusplus/aflplusplus Docker image, and a harness or a program that reads stdin, files, or argv.
  • Optional: Seed corpus directory. It may be empty; when omitted, create ./corpus/ (libfuzzer) or seeds/ with one non-empty file (afl).
  • Optional: Fuzzing dictionary file (see Dictionary format below).
  • Optional (libfuzzer): Clang build flags: -fsanitize=address, -fsanitize=undefined, -g, -O2, -max_len, -dict, -timeout, -close_fd_mask, -fork, -ignore_crashes.
  • Optional (afl): run location host or Docker (default Docker); instrumentation mode LTO, LLVM, or GCC (default tries LTO, falls back to LLVM); core count (default single instance); sanitizer selection ASan, UBSan, or none (default none).

Read the full file on GitHub · 133 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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.

  1. 2d ago First seen · 133 lines · 45 tokens per session scan A 1a63b067a964

Subscribe to this mod's changes

libfuzzer is a skill published in the GitHub repository OutlineDriven/odin-claude-plugin (35 stars, last pushed yesterday), licensed Apache-2.0. It adds 45 tokens to every session and 3,789 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 2026-09-06.

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