Web Quality Skills

An (unofficial) measurement-first collection of Agent Skills for optimizing web projects with Google Lighthouse, Chrome DevTools for agents, Core Web Vitals, WCAG, and search guidance.

Stack-agnostic. Works with any framework: React, Vue, Angular, Svelte, Next.js, Nuxt, Astro, plain HTML, and more.

Why web quality skills?

While interface guidelines tell you what to build, Web Quality Skills tell you how to build it performantly, accessibly, and optimally for search engines. These skills combine:

• Live Lighthouse audits for agents across Accessibility, SEO, Best Practices, and Agentic Browsing when Chrome DevTools MCP is available
• Performance traces and Insights for diagnosing LCP, INP, CLS, network, and main-thread bottlenecks
• Field plus lab measurement using CrUX for real-user context and controlled browser runs for repeatable diagnosis
• Core Web Vitals optimization patterns for LCP, INP, and CLS
• WCAG 2.2 accessibility standards
• Modern SEO requirements

Available skills

Measurement model

The performance skills keep four evidence types explicit:

Field data determines user impact. Lab traces reproduce and diagnose it. A PerformanceObserver snippet run in one browser is a lab observation, not real-user data by itself.

Quick start

Installation

add-skill is a powerful CLI tool that lets you install agent skills onto your coding agents from git repositories. Whether you're using OpenCode, Claude Code, Codex, or Cursor, the add-skill tool makes it simple to extend your agent's capabilities with specialized instruction sets. Use add-skill to automate release notes, create pull requests, integrate with external tools, and more. Simply run npx add-skill to get started.

npx skills add addyosmani/web-quality-skills

or

npx add-skill addyosmani/web-quality-skills

Or manually:

cp -r skills/* ~/.claude/skills/

Claude Code (plugin)

Install as a versioned, namespaced plugin from inside Claude Code:

/plugin marketplace add addyosmani/web-quality-skills
/plugin install web-quality-skills@addy-web-quality-skills

Skills are then namespaced (e.g. /web-quality-skills:performance) and update with /plugin update. The plugin reads the same skills/ directory as the manual copy above — no duplication.

Codex

Install directly via the Codex plugin marketplace (Codex CLI v0.122+):

codex plugin marketplace add addyosmani/web-quality-skills

Once installed, invoke skills in chat using @ (e.g. @performance, @accessibility). See docs/codex-setup.md for local installation and troubleshooting.

Gemini CLI

Install directly via Gemini CLI extensions:

gemini extensions install https://github.com/addyosmani/web-quality-skills

Skills are auto-discovered by Gemini and activate when prompts match their description. See docs/gemini-setup.md for workspace mode and troubleshooting.

claude.ai

Add skills to your project knowledge or paste the SKILL.md contents into your conversation.

Usage

Skills activate automatically when your request matches their description. Examples:

Audit this page for web quality issues

Optimize performance and fix Core Web Vitals

Review accessibility and suggest improvements

Make this SEO-ready

Optional Chrome DevTools integration

When the agent exposes equivalent live-browser capabilities, the skills prefer them. With Chrome DevTools MCP, the current tool names are:

• performance_start_trace and focused Performance Insights for performance work, including CrUX context when eligible field data exists
• lighthouse_audit for Accessibility, SEO, Best Practices, and Agentic Browsing
• rendered accessibility snapshots, console messages, and network requests for issue-level diagnosis

This integration is optional. Without it, the skills fall back to Lighthouse CLI, PageSpeed Insights/CrUX tools, manual browser checks, and static inspection rather than stopping the task.

Skill details

web-quality-audit

The comprehensive skill that orchestrates all other skills. It starts with live evidence when a page is runnable and keeps measured failures separate from source-code hypotheses.

Trigger phrases: "audit my site", "quality review", "lighthouse audit", "check web quality"

What it checks:

• All Core Web Vitals metrics
• Performance Insights, network delivery, and runtime bottlenecks
• Automated and manual accessibility signals
• Crawl, index, metadata, and structured-data requirements
• Security, compatibility, and browser best-practice patterns
• Agentic Browsing signals such as agent-facing semantics and optional WebMCP/llms.txt checks

performance

Deep-dive into loading and runtime performance optimization, using CrUX or first-party RUM to prioritize user impact and DevTools traces to diagnose causes.

Trigger phrases: "speed up", "optimize performance", "reduce load time", "fix slow"

Key optimizations:

• Critical rendering path
• JavaScript bundling and code splitting
• Image optimization (formats, sizing, lazy loading)
• Font loading strategies
• Caching and preloading
• Server response optimization

core-web-vitals

Specialized skill for the three Core Web Vitals that describe loading, responsiveness, and visual stability. Google uses Core Web Vitals in its page-experience systems, but a passing score does not promise a ranking change.

Trigger phrases: "Core Web Vitals", "LCP", "INP", "CLS", "page experience"

Metrics covered:

• LCP (Largest Contentful Paint) < 2.5s
• INP (Interaction to Next Paint) < 200ms
• CLS (Cumulative Layout Shift) < 0.1

accessibility

Comprehensive accessibility audit following WCAG 2.2 guidelines.

Trigger phrases: "accessibility", "a11y", "WCAG", "screen reader", "keyboard navigation"

Categories:

• Perceivable (text alternatives, captions, contrast)
• Operable (keyboard, timing, seizures, navigation)
• Understandable (readable, predictable, input assistance)
• Robust (compatible with assistive technologies)

seo

Search engine optimization for better visibility and ranking.

Trigger phrases: "SEO", "search optimization", "meta tags", "structured data", "sitemap"

What it covers:

• Technical SEO (crawlability, indexability)
• On-page SEO (meta tags, headings, content structure)
• Structured data (JSON-LD, schema.org)
• Mobile-friendliness
• Performance signals

best-practices

Modern web development standards and security practices.

Trigger phrases: "best practices", "security audit", "modern standards", "code quality"

Areas covered:

• HTTPS and security headers
• Modern JavaScript APIs
• Browser compatibility
• Error handling
• Console cleanliness

Thresholds reference

Core Web Vitals

Field Core Web Vitals are assessed at the 75th percentile; these thresholds are not a claim about a single lab run.

Starting performance budget recommendations

These are initial guardrails, not universal thresholds. Set budgets from the product's target devices, networks, page types, and user journeys.

Example automated audit guardrails

Scores help catch regressions but do not prove accessibility, security, SEO ranking, or user experience. Preserve project-specific targets and compare runs made with the same tool version and conditions.

Framework-specific notes

These skills are framework-agnostic, but some common patterns:

React/Next.js: Use next/image, React.lazy(), Suspense, useCallback/useMemo for INP
Vue/Nuxt: Use nuxt/image, async components, v-once, computed properties
Svelte/SvelteKit: Use {#await}, svelte:image, reactive statements
Astro: Use <Image>, partial hydration, view transitions
Static HTML: Use native lazy loading, <picture>, preconnect hints

Contributing

Contributions welcome! Please follow the Agent Skills specification.

1. Fork the repository
2. Create your skill in skills/{skill-name}/SKILL.md
3. Keep SKILL.md under 500 lines (use references/ for details)
4. Include practical examples and patterns
5. Submit a pull request

Resources

• Google Lighthouse Documentation
• Lighthouse audits with AI agents
• Chrome DevTools MCP
• Chrome UX Report
• web.dev Learn Performance
• Core Web Vitals
• WCAG 2.2 Guidelines
• Agent Skills Specification

License

MIT License - see LICENSE for details.

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Built with insights from the Chrome DevTools team, web performance experts, and accessibility advocates to help developers create high-quality web experiences.