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Agent skill

Experimental Code Coverage Local Debugger

by nwjs in nwjs/chromium.src

Runs code coverage locally via Universal Test Runner (UTR) or helper scripts, mimicking LUCI trybots.

BSD-3-ClauseAuto-check passedTesting & QA

Install Experimental Code Coverage Local Debugger

skills CLI
$ npx skills add nwjs/chromium.src --skill experimental-code-coverage-local-debugger -a claude-code

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

GitHub CLI
$ gh skill install nwjs/chromium.src experimental-code-coverage-local-debugger --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/experimental-code-coverage-local-debugger .claude/skills/experimental-code-coverage-local-debugger && 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/

Facts

Skill name
experimental-code-coverage-local-debugger
GitHub stars
160
Token cost
~989 tokens
SKILL.md length
352 words
Files
1
Skills in repo
64
Repo updated
First seen
Licence
BSD-3-Clause

At a glance

Runs code coverage locally via Universal Test Runner (UTR) or helper scripts, mimicking LUCI trybots.

  • Works in 4 steps: Regenerate Starlark Configurations → Execute Universal Test Runner (UTR) → Rapid Workstation Execution (Bypass… → …
  • Tasks that involve Test coverage
  • SKILL.md covers When to Use This Skill, Inputs, Workflow and References
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Experimental Code Coverage Local Debugger is an agent skill from nwjs/chromium.src. Runs code coverage locally via Universal Test Runner (UTR) or helper scripts, mimicking LUCI trybots. Activate when CQ tryjobs fail or underreport coverage, to test local GN/recipe repairs before uploading, or to debug hermetic crashes.

Its SKILL.md is about 990 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Testing & QA, covering Test coverage. 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

  • Tasks that involve Test coverage

Example prompts

  • “/experimental-code-coverage-local-debugger”

Workflow steps

4 steps, taken from the step headings in SKILL.md.

  1. Regenerate Starlark Configurations
  2. Execute Universal Test Runner (UTR)
  3. Rapid Workstation Execution (Bypass Container)
  4. Inspect Local Verification Artifacts

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).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    Links to these hosts (documentation or services it may open):

    • clang.llvm.org
    • chromium.googlesource.com

    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

Experimental Code Coverage Local Debugger loads about 989 tokens when it runs. Until then it costs about 70 tokens; SKILL.md has 352 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~70
When it runs · the whole SKILL.md, loaded when a task matches
~989

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). 352 words, ~989 tokens.

Download SKILL.mdSave it as .claude/skills/experimental-code-coverage-local-debugger/SKILL.md (or your agent's skills folder).
name
experimental-code-coverage-local-debugger
description
Runs code coverage locally via Universal Test Runner (UTR) or helper scripts, mimicking LUCI trybots. Activate when CQ tryjobs fail or underreport coverage, to test local GN/recipe repairs before uploading, or to debug hermetic crashes.

Code Coverage Local Debugger

Use this skill to generate code coverage data on a local workstation using Chromium's Universal Test Runner (tools/utr). It wraps the exact recipe logic used by LUCI trybots, dynamically evaluating local Starlark and GN repairs.

When to Use This Skill

  • Automated tryjobs fail or underreport coverage on CQ.
  • Testing whether local GN argument or Starlark recipe repairs successfully restore code coverage before uploading patchsets.
  • Isolating whether test suite crashes occur in local hermetic environments.

Inputs

  • builder_name: The target CQ builder name (e.g., "linux-rel").
  • bucket: The builder bucket (default: "try").
  • test_suite: The target test target name (e.g., "net_unittests").
  • build_dir: Optional custom output directory (e.g., "out/Coverage").

Workflow

1. Regenerate Starlark Configurations

If prior agent debugging steps modified Starlark files under infra/config/, regenerate the global configuration files so UTR reads the latest state.

bash
lucicfg generate infra/config/main.star
2. Execute Universal Test Runner (UTR)

For general UTR command documentation, common flags, and authentication guidelines, refer to the utr skill.

When debugging code coverage specifically, invoke tools/utr/run.py to compile and execute the test target while replicating the exact LUCI builder recipe environment and evaluating Starlark code coverage GN arguments (e.g., use_clang_coverage = true):

bash
vpython3 tools/utr/run.py -p chromium -B {{bucket}} -b {{builder_name}} \
  -t {{test_suite}} compile-and-test
  • When to Use UTR for Code Coverage: Use this option when you need to verify that Starlark or GN argument repairs successfully restore code coverage instrumentation and .profdata generation before uploading a CL, or when isolating shard failures on platforms not accessible locally (e.g., Windows or ChromeOS).
Show full SKILL.md (118 more words)Show less
3. Rapid Workstation Execution (Bypass Container)

To build and run a native workstation test binary directly against pinned LLVM tools without UTR container overhead, execute run_local_coverage.py:

bash
vpython3 tools/code_coverage/run_local_coverage.py \
  --binary {{build_dir}}/{{test_suite}} --source {{target_file}}
  • Automatic Compilation: run_local_coverage.py automatically compiles the target test binary using autoninja -C {{build_dir}} {{test_suite}} before running.
  • Pre-built Binary Optimization: Pass --no-compile if the target binary is already compiled locally to skip the build step.
4. Inspect Local Verification Artifacts
  • Inspect Artifacts: Audit ResultDB / Milo links printed at the end of the UTR run (ci.chromium.org/ui/inv/...) to verify code coverage percentage resolution.
  • Symbol Validation: For rapid helper runs (run_local_coverage.py), verify that generated .profdata reports non-zero line execution counts matching edits.

References

© nwjs, BSD-3-Clause. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in agents/skills/experimental-code-coverage-local-debugger of nwjs/chromium.src.

Open the folder on GitHubat commit a9e8946

Compare with similar skills

Experimental Code Coverage Local Debugger 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.

Experimental Code Coverage Local Debugger compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Experimental Code Coverage Local Debugger this skillnwjs/chromium.src160—~989Automated safety check: PassBSD-3-Clause
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Crap Analysisardalis/RiverBooks1352 repos~3.4kAutomated safety check: PassNone
Code Coverages3s-project/s3s311—~789Automated safety check: PassApache-2.0
Project Statusbactopia/bactopia522—~787Automated safety check: PassMIT
Check Coverageldayton/Dippy243—~403Automated safety check: PassMIT

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Categories

Questions about Experimental Code Coverage Local Debugger

What does Experimental Code Coverage Local Debugger do?

Runs code coverage locally via Universal Test Runner (UTR) or helper scripts, mimicking LUCI trybots. src. Runs code coverage locally via Universal Test Runner (UTR) or helper scripts, mimicking LUCI trybots.

When should I use Experimental Code Coverage Local Debugger?

Experimental Code Coverage Local Debugger fits situations like: tasks that involve Test coverage.

How do I install Experimental Code Coverage Local Debugger in Claude Code?

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

How do I install Experimental Code Coverage Local Debugger in Codex?

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

Can I use Experimental Code Coverage Local Debugger 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 experimental-code-coverage-local-debugger -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/experimental-code-coverage-local-debugger, .gemini/skills/experimental-code-coverage-local-debugger, .github/skills/experimental-code-coverage-local-debugger and .opencode/skills/experimental-code-coverage-local-debugger in your project.

What does Experimental Code Coverage Local Debugger need to run?

SKILL.md names no scripts, command-line tools or credentials: Experimental Code Coverage Local Debugger is instructions for the agent only.

Does Experimental Code Coverage Local Debugger access the network?

SKILL.md names 2 domains. As links in the text: clang.llvm.org and chromium.googlesource.com. This is read from the text; nothing was executed.

Is Experimental Code Coverage Local Debugger 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 Experimental Code Coverage Local Debugger use?

Experimental Code Coverage Local Debugger 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 Experimental Code Coverage Local Debugger use?

About 989 tokens (SKILL.md is roughly 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 Experimental Code Coverage Local Debugger?

Skills that share tags, products or a category with Experimental Code Coverage Local Debugger: Requirements (rizsotto/Bear, 6.5k stars), Crap Analysis (ardalis/RiverBooks, 135 stars), Code Coverage (s3s-project/s3s, 311 stars) and Project Status (bactopia/bactopia, 522 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Experimental Code Coverage Local Debugger?

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.