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Agent skill

Experimental Code Coverage Swarming Output Validator

by nwjs in nwjs/chromium.src

Validates code coverage Swarming execution logs, CAS input/output profile artifacts, and profile generation environments to isolate remote trybot code coverage failures.

BSD-3-ClauseAuto-check passedTesting & QA

Install Experimental Code Coverage Swarming Output Validator

skills CLI
$ npx skills add nwjs/chromium.src --skill experimental-code-coverage-swarming-output-validator -a claude-code

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

GitHub CLI
$ gh skill install nwjs/chromium.src experimental-code-coverage-swarming-output-validator --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-swarming-output-validator .claude/skills/experimental-code-coverage-swarming-output-validator && 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-swarming-output-validator
GitHub stars
160
Token cost
~1.2k tokens
SKILL.md length
442 words
Files
1
Skills in repo
64
Repo updated
First seen
Licence
BSD-3-Clause

At a glance

Validates code coverage Swarming execution logs, CAS input/output profile artifacts, and profile generation environments to isolate remote trybot code coverage failures.

  • Works in 5 steps: Extract Task Digests & Swarming Task IDs → Fast Remote Output Audit → Pre-Run CAS Input Audit → …
  • Tasks that involve Test coverage
  • SKILL.md covers When to Use This Skill, Inputs and Workflow
  • Reaches ci.chromium.org

What it does

Experimental Code Coverage Swarming Output Validator is an agent skill from nwjs/chromium.src. Validates code coverage Swarming execution logs, CAS input/output profile artifacts, and profile generation environments to isolate remote trybot code coverage failures.

Its SKILL.md is about 1.2k 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

  • “Use the experimental-code-coverage-swarming-output-validator skill to validate code coverage Swarming execution logs, CAS input/output profile…”
  • “/experimental-code-coverage-swarming-output-validator”

Requirements

  • Python 3

Workflow steps

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

  1. Extract Task Digests & Swarming Task IDs
  2. Fast Remote Output Audit
  3. Pre-Run CAS Input Audit
  4. Hermetic Container Replay
  5. Generate Summary Artifact

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

    Hosts in commands or code, which the agent is likely to contact:

    • ci.chromium.org

    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 Swarming Output Validator loads about 1.2k tokens when it runs. Until then it costs about 56 tokens; SKILL.md has 442 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~56
When it runs · the whole SKILL.md, loaded when a task matches
~1.2k

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). 442 words, ~1,228 tokens.

Download SKILL.mdSave it as .claude/skills/experimental-code-coverage-swarming-output-validator/SKILL.md (or your agent's skills folder).
name
experimental-code-coverage-swarming-output-validator
description
Validates code coverage Swarming execution logs, CAS input/output profile artifacts, and profile generation environments to isolate remote trybot code coverage failures.

Code Coverage Swarming Output Validator

Use this skill exclusively to audit remote Swarming bot executions for code coverage on Chromium tryjobs. It validates whether code coverage profile artifacts (.profraw) were generated and returned to Content Addressable Storage (CAS), verifies isolate packaging dependencies, and reproduces shard executions inside pinned LUCI containers.

When to Use This Skill

  • Diagnosing why code coverage numbers dropped or returned empty profiles on CQ.
  • Verifying whether a remote Swarming shard successfully produced .profraw outputs before attempting slow local compilations.
  • Auditing CAS isolate inputs (.isolate, test_env.py) for missing data deps.
  • Replaying a Swarming shard locally inside LUCI's hermetic CIPD/Python runtime.

Inputs

This skill requires the following inputs:

  • swarming_server: The Swarming host (default: "chromium-swarm.appspot.com").
  • cas_instance: The CAS instance name (default: "projects/chromium-swarm/instances/default_instance").
  • test_suites: The target test suites list (e.g., ["net_unittests", "browser_tests"]).
  • build_url: The Buildbucket build URL/link or build ID (e.g., "https://ci.chromium.org/b/8679...").

Workflow

1. Extract Task Digests & Swarming Task IDs

First, resolve the numeric Buildbucket build ID (build_id) from build_url. Note that LUCI URLs may use direct Buildbucket IDs (/b/8679...) or sequential builder paths (.../builders/try/linux-rel/2772707/...). When given a builder path URL, pass the canonical builder path (chromium/try/linux-rel/2772707) directly to bb get or use the buildbucket skill to resolve the numeric build ID.

Then, for each test suite in test_suites, invoke the standalone extraction helper script tools/code_coverage/get_task_digest.py passing build_id:

bash
vpython3 tools/code_coverage/get_task_digest.py \
  --build {{build_id}} --step <test_suite>

This helper prints JSON containing the swarming_task_id and cas_input_digest for each target test suite.

Show full SKILL.md (227 more words)Show less
2. Fast Remote Output Audit

For each extracted swarming_task_id, download and audit only the CAS output artifacts returned by the bot shard. This verifies remote execution integrity with zero local compilation.

bash
mkdir -p scratch/swarm_out
vpython3 third_party/depot_tools/swarming.py collect \
  -S chromium-swarm.appspot.com -output-dir=scratch/swarm_out \
  {{swarming_task_id}}
  • Profile Audit: Check if .profraw files exist in scratch/swarm_out/.
  • Merge Check: Run llvm-profdata show on downloaded profile data:
    bash
    third_party/llvm-build/Release+Asserts/bin/llvm-profdata show \
  scratch/swarm_out/profraw/*.profraw
  • Diagnosis:
    • Empty / ~2 Functions: If function count is abnormally low (e.g., only 2 Rust wrapper functions instead of thousands of C++ functions), immediately diagnose a Remote Siso/Recipe Collection Bug. The test executed remotely, but Siso/RBE failed to return intermediate profile artifacts.
3. Pre-Run CAS Input Audit

If remote outputs are missing entirely, audit the uploaded CAS input root to confirm whether GN data_deps bundled required runtime files.

  • Download the isolate bundle using cas_input_digest:
    bash
    mkdir -p scratch/cas_in
cas download \
  -cas-instance projects/chromium-swarm/instances/default_instance \
  -digest {{cas_input_digest}} -dir scratch/cas_in
  • Inspect .isolate mappings and test_env.py to ensure profile environment variables (LLVM_PROFILE_FILE) are properly initialized.
4. Hermetic Container Replay

If remote profiles are corrupt or crash on the bot, replay the exact shard run locally on your workstation inside LUCI's pinned CIPD/Python environment using swarming_task_id.

bash
mkdir -p scratch/container_repro && cd scratch/container_repro
vpython3 ../../third_party/depot_tools/swarming.py reproduce \
  -S chromium-swarm.appspot.com {{swarming_task_id}}
  • Note: This abstracts away local OS differences and runs the test binary inside the exact virtualenv used by the LUCI compilator bot.
5. Generate Summary Artifact

Create a summary document of all steps taken, swarming task IDs, .profraw file existence/integrity, and diagnostic findings at scratch/swarming_summary.md.

© 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-swarming-output-validator of nwjs/chromium.src.

Open the folder on GitHubat commit a9e8946

Compare with similar skills

Experimental Code Coverage Swarming Output Validator 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 Swarming Output Validator compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Experimental Code Coverage Swarming Output Validator this skillnwjs/chromium.src160—~1.2kAutomated 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 Swarming Output Validator

What does Experimental Code Coverage Swarming Output Validator do?

Validates code coverage Swarming execution logs, CAS input/output profile artifacts, and profile generation environments to isolate remote trybot code coverage failures. src. Validates code coverage Swarming execution logs, CAS input/output profile artifacts, and profile generation environments to isolate remote trybot code coverage failures.

When should I use Experimental Code Coverage Swarming Output Validator?

Experimental Code Coverage Swarming Output Validator fits situations like: tasks that involve Test coverage.

How do I install Experimental Code Coverage Swarming Output Validator in Claude Code?

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

How do I install Experimental Code Coverage Swarming Output Validator in Codex?

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

Can I use Experimental Code Coverage Swarming Output Validator 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-swarming-output-validator -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-swarming-output-validator, .gemini/skills/experimental-code-coverage-swarming-output-validator, .github/skills/experimental-code-coverage-swarming-output-validator and .opencode/skills/experimental-code-coverage-swarming-output-validator in your project.

What does Experimental Code Coverage Swarming Output Validator need to run?

SKILL.md names no scripts, command-line tools or credentials: Experimental Code Coverage Swarming Output Validator is instructions for the agent only. Our summary lists: Python 3.

Does Experimental Code Coverage Swarming Output Validator access the network?

SKILL.md names 1 domain. In commands or code: ci.chromium.org; the agent is likely to contact it when it follows the instructions. This is read from the text; nothing was executed.

Is Experimental Code Coverage Swarming Output Validator 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 Swarming Output Validator use?

Experimental Code Coverage Swarming Output Validator 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 Swarming Output Validator use?

About 1.2k tokens (SKILL.md is roughly 4.9k 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 Swarming Output Validator?

Skills that share tags, products or a category with Experimental Code Coverage Swarming Output Validator: 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 Swarming Output Validator?

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.