Agent skill

Fuzzing

Implements, registers, and verifies fuzz tests in Chromium. An agent skill from nwjs/chromium.src.

BSD-3-ClauseAuto-check passedSecurity

Install Fuzzing

skills CLI

$ npx skills add nwjs/chromium.src --skill fuzzing -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install nwjs/chromium.src fuzzing --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/nwjs/chromium.src.git skills-src && mkdir -p .claude/skills && cp -r skills-src/agents/skills/fuzzing .claude/skills/fuzzing && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "fuzzing" agent skill from https://github.com/nwjs/chromium.src/tree/main/agents/skills/fuzzing into .claude/skills/fuzzing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "fuzzing", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/nwjs/chromium.src/tree/main/agents/skills/fuzzing

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add nwjs/chromium.src --skill fuzzing -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install nwjs/chromium.src fuzzing --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/nwjs/chromium.src.git skills-src && mkdir -p .agents/skills && cp -r skills-src/agents/skills/fuzzing .agents/skills/fuzzing && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "fuzzing" agent skill from https://github.com/nwjs/chromium.src/tree/main/agents/skills/fuzzing into .agents/skills/fuzzing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "fuzzing", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add nwjs/chromium.src --skill fuzzing -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install nwjs/chromium.src fuzzing --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/nwjs/chromium.src.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/agents/skills/fuzzing .cursor/skills/fuzzing && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "fuzzing" agent skill from https://github.com/nwjs/chromium.src/tree/main/agents/skills/fuzzing into .cursor/skills/fuzzing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "fuzzing", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/nwjs/chromium.src.git --path agents/skills/fuzzing

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add nwjs/chromium.src --skill fuzzing -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install nwjs/chromium.src fuzzing --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/nwjs/chromium.src.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/agents/skills/fuzzing .gemini/skills/fuzzing && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "fuzzing" agent skill from https://github.com/nwjs/chromium.src/tree/main/agents/skills/fuzzing into .gemini/skills/fuzzing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "fuzzing", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install nwjs/chromium.src fuzzing

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add nwjs/chromium.src --skill fuzzing -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/nwjs/chromium.src.git skills-src && mkdir -p .github/skills && cp -r skills-src/agents/skills/fuzzing .github/skills/fuzzing && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "fuzzing" agent skill from https://github.com/nwjs/chromium.src/tree/main/agents/skills/fuzzing into .github/skills/fuzzing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "fuzzing", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add nwjs/chromium.src --skill fuzzing -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install nwjs/chromium.src fuzzing --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/nwjs/chromium.src.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/agents/skills/fuzzing .opencode/skills/fuzzing && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "fuzzing" agent skill from https://github.com/nwjs/chromium.src/tree/main/agents/skills/fuzzing into .opencode/skills/fuzzing/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "fuzzing", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: fuzzing
GitHub stars: 160
Token cost: ~1.1k tokens
SKILL.md length: 264 words
Files: 2
Skills in repo: 64
Repo updated: Oct 3, 2026
First seen: Oct 8, 2026
Licence: BSD-3-Clause

At a glance

Implements, registers, and verifies fuzz tests in Chromium. An agent skill from nwjs/chromium.src.

The user asks to add
SKILL.md covers 1. Setup, Resources and Common Issues & Fixes
Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
Write fuzzers in C++

What it does

Fuzzing is an agent skill from nwjs/chromium.src. Implements, registers, and verifies fuzz tests in Chromium. Use when the user asks to add or write fuzzers in C++, or mentions fuzz testing or FUZZTEST.

Its SKILL.md is about 1.1k tokens, which your agent loads only when the skill is triggered. The skill folder holds 1 other file.

It sits in Security, covering Fuzzing. It works with C++. The repository describes itself as: Chromium codebase with NW.js modifications. Based on https://chromium.googlesource.com/chromium/src.git. The licence is BSD-3-Clause.

When your agent uses it

The user asks to add
Write fuzzers in C++
Mentions fuzz testing

Example prompts

“/fuzzing”

Requirements

Python 3

What it can do on your machine

Read from SKILL.md and the folder at commit a9e8946. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md (its code samples are bash, cpp, gn and python).
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Fuzzing loads about 1.1k tokens when it runs. Until then it costs about 40 tokens; SKILL.md has 264 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~40
When it runs · the whole SKILL.md, loaded when a task matches: ~1.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from nwjs/chromium.src at commit a9e8946, republished under its BSD-3-Clause licence (© nwjs). 264 words, ~1,101 tokens.

Download SKILL.mdSave it as .claude/skills/fuzzing/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.

name: fuzzing
description: Implements, registers, and verifies fuzz tests in Chromium. Use when the user asks to add or write fuzzers in C++, or mentions fuzz testing or FUZZ_TEST.

Fuzzing (Chromium)

1. Setup

Ensure the output directory is configured:

bash

gn gen out/fuzz --args='enable_fuzztest_fuzz=true is_debug=false is_asan=true \
is_component_build=false use_remoteexec=true'

2. Implement the FUZZ_TEST

Add to *_unittest.cc alongside existing tests:

cpp

#include "third_party/fuzztest/src/fuzztest/fuzztest.h"
#include "third_party/googletest/src/googletest/include/gtest/gtest.h"

// 1. Define the property function. Use a descriptive name that reflects
// the property being tested (e.g., "ParseFooDoesNotCrash" or "RoundTripIsLossless").
void MyPropertyFunctionDoesNotCrash(int i, const std::string& s) {
  // Call code under test. Focus on functions parsing untrusted input, complex
  // state machines, or data processing.
  bool result = MyComponent::DoSomething(i, s);
  // Add test assertions about invariants (e.g. "roundtrip equality", "valid
  // output structure"). Sanitizers like ASAN catch crashes.
  EXPECT_TRUE(result);
}

// 2. Register with FUZZ_TEST macro
FUZZ_TEST(MyComponentFuzzTest, MyPropertyFunctionDoesNotCrash)
  .WithDomains(
      fuzztest::InRange(0, 100),
      fuzztest::Arbitrary<std::string>()
  );

For complex types:

Construct from primitives: If the object has a parsing constructor (e.g. GURL(string)), accept the primitive and construct it inside your test function.
Define a local domain: Use fuzztest::Constructor or fuzztest::Map to build valid objects.
cpp
```
auto ArbitraryFoo() {
  return fuzztest::Constructor<Foo>(fuzztest::InRange(0, 10));
}
```

3. Register in BUILD.gn

You MUST register the test in the fuzztests list (in alphabetical order) of the executable test target.

Case A: File is in a test() target

test("my_component_unittests") {
  sources = [ "my_component_unittest.cc" ]

  # Format: SuiteName.TestName
  fuzztests = [
    "MyComponentFuzzTest.MyPropertyFunctionDoesNotCrash",
  ]

  # No dependency changes are needed here. The build system
  # automatically adds FuzzTest dependencies for targets
  # with a `fuzztests` list.

}

Case B: File is in a source_set(): Add //third_party/fuzztest:fuzztest to deps.

source_set("tests") {
  sources = [ "my_component_unittest.cc" ]
  deps = [
    "//third_party/fuzztest:fuzztest",
    # ...
  ]
}

Find the executable test() target that depends on this source_set(): gn refs out/fuzz //path/to:source_set --testonly=true --type=executable --all

Then, ensure it lists the fuzz test in its fuzztests variable (in alphabetical order).

4. Mandatory verification workflow

The task is incomplete until you successfully execute this sequence:

Find the target and Build

Find the executable test() target that contains your test file:

bash

gn refs out/fuzz //path/to/my_component_unittest.cc --type=executable --all

Build the identified target (e.g. unit_tests or browser_tests):

bash

autoninja --quiet -C out/fuzz <target_name>

Note: If the build fails with an include not allowed by DEPS error, see the Common Issues & Fixes section below.

Verify unit tests pass

bash

./out/fuzz/<target_name> \
--gtest_filter="MyComponentFuzzTest.MyPropertyFunctionDoesNotCrash"

Verify fuzzing mode doesn't crash

bash

./out/fuzz/<target_name> \
--fuzz="MyComponentFuzzTest.MyPropertyFunctionDoesNotCrash" --fuzz_for=10s

Resources

Chromium Guide: testing/libfuzzer/getting_started.md
Macro Usage: third_party/fuzztest/src/doc/fuzz-test-macro.md
Domains: third_party/fuzztest/src/doc/domains-reference.md
Fixtures: third_party/fuzztest/src/doc/fixtures.md

Common Issues & Fixes

Build failure: include not allowed by DEPS

Symptom: Build fails with an error like: ERROR: include not allowed by DEPS: third_party/fuzztest/...

Fix: You must allow the fuzztest include in the nearest DEPS file (usually in the same directory as your test or a parent directory). Add +third_party/fuzztest to specific_include_rules for your test files:

python

specific_include_rules = {
  ".*_unittest\\.cc": [
    "+third_party/fuzztest",
  ],
}

Files

SKILL.md and 1 other file in agents/skills/fuzzing of nwjs/chromium.src.

SKILL.md
OWNERS

Open the folder on GitHubat commit a9e8946

Compare with similar skills

Fuzzing next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Fuzzing compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
Fuzzing this skillnwjs/chromium.src	160	—	~1.1k	Automated safety check: Pass	BSD-3-Clause	4 days ago
Harness Design Fuzzingprovos/ironcurtain	613	—	~5.7k	Automated safety check: Pass	Apache-2.0	yesterday
ClusterfuzzliteInternationalColorConsortium/iccDEV	183	—	~1.5k	Automated safety check: Pass	BSD-3-Clause	today
Fuzzing Harness Designtrailofbits/skills	7.4k	1 repos	~5.3k	Automated safety check: Pass	CC-BY-SA-4.0	yesterday
Fuzzing Obstacle Patchertrailofbits/skills	7.4k	—	~4k	Automated safety check: Pass	CC-BY-SA-4.0	yesterday
Aflpptrailofbits/skills	7.4k	—	~5.6k	Automated safety check: Pass	CC-BY-SA-4.0	yesterday

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Queries Chrome commit, version, release, and milestone metadata.
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Chromium Docs
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Search and reference Chromium documentation from the local docs index, including design docs, APIs, and development guides.
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Works with

Questions about Fuzzing

What does Fuzzing do?

Implements, registers, and verifies fuzz tests in Chromium. An agent skill from nwjs/chromium.src. src. Implements, registers, and verifies fuzz tests in Chromium.

When should I use Fuzzing?

Fuzzing fits situations like: the user asks to add; write fuzzers in C++; mentions fuzz testing.

How do I install Fuzzing in Claude Code?

Run `npx skills add nwjs/chromium.src --skill fuzzing -a claude-code`. Or copy the skill folder (agents/skills/fuzzing in nwjs/chromium.src) into .claude/skills/fuzzing in your project. Claude Code loads it when a task matches its description.

How do I install Fuzzing in Codex?

Run `npx skills add nwjs/chromium.src --skill fuzzing -a codex`. Or copy the skill folder (agents/skills/fuzzing in nwjs/chromium.src) into .agents/skills/fuzzing in your project. Codex loads it when a task matches its description.

Can I use Fuzzing in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add nwjs/chromium.src --skill fuzzing -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/fuzzing, .gemini/skills/fuzzing, .github/skills/fuzzing and .opencode/skills/fuzzing in your project.

What does Fuzzing need to run?

SKILL.md names no scripts, command-line tools or credentials: Fuzzing is instructions for the agent only. Our summary lists: Python 3.

Does Fuzzing access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Fuzzing safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Fuzzing use?

Fuzzing is published under the BSD-3-Clause licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Fuzzing use?

About 1.1k tokens (SKILL.md is roughly 4.4k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Fuzzing?

Skills that share tags, products or a category with Fuzzing: Harness Design Fuzzing (provos/ironcurtain, 613 stars), Clusterfuzzlite (InternationalColorConsortium/iccDEV, 183 stars), Fuzzing Harness Design (trailofbits/skills, 7.4k stars) and Fuzzing Obstacle Patcher (trailofbits/skills, 7.4k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Fuzzing?

nwjs (a GitHub organization) maintains it in nwjs/chromium.src, which has 160 GitHub stars. The repository holds 64 skills in this directory. The repository was last updated on October 3, 2026.

Source: nwjs/chromium.src on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Install Fuzzing

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Fuzzing (Chromium)

1. Setup

2. Implement the FUZZ_TEST

3. Register in BUILD.gn

4. Mandatory verification workflow

Resources

Common Issues & Fixes

Build failure: include not allowed by DEPS

Files

Compare with similar skills

Similar skills

More from nwjs/chromium.src

Related

Questions about Fuzzing