Web Quality Skills

An (unofficial) comprehensive collection of Agent Skills for optimizing web projects based on Google Lighthouse guidelines and Core Web Vitals best practices.

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 encode the collective wisdom from:

• 150+ Lighthouse audits across Performance, Accessibility, SEO, and Best Practices
• Core Web Vitals optimization patterns (LCP, INP, CLS)
• Real-world performance engineering experience
• WCAG 2.1 accessibility standards
• Modern SEO requirements

Available skills

| Skill | Description | Use when | |-------|-------------|----------| | web-quality-audit | Comprehensive quality review across all categories | "Audit my site", "Review this for quality", "Check web quality" | | performance | Loading speed, runtime efficiency, resource optimization | "Optimize performance", "Speed up my site", "Fix slow loading" | | core-web-vitals | LCP, INP, CLS specific optimizations | "Improve Core Web Vitals", "Fix LCP", "Reduce CLS" | | accessibility | WCAG compliance, screen reader support, keyboard navigation | "Improve accessibility", "WCAG audit", "a11y review" | | seo | Search engine optimization, crawlability, structured data | "Optimize for SEO", "Improve search ranking", "Fix meta tags" | | best-practices | Security, modern APIs, code quality patterns | "Apply best practices", "Security audit", "Code quality review" |

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 add-skill addyosmani/web-quality-skills

Or manually:

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

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

Skill details

web-quality-audit

The comprehensive skill that orchestrates all other skills. Use this for full-site audits or when you're unsure which specific area needs attention.

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

What it checks:

• All Core Web Vitals metrics
• 50+ performance patterns
• 40+ accessibility rules
• 30+ SEO requirements
• 20+ security/best practice patterns

performance

Deep-dive into loading and runtime performance optimization.

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 affect Google Search ranking.

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 2.1 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

| Metric | Good | Needs improvement | Poor | |--------|------|-------------------|------| | LCP | ≤ 2.5s | 2.5s – 4.0s | > 4.0s | | INP | ≤ 200ms | 200ms – 500ms | > 500ms | | CLS | ≤ 0.1 | 0.1 – 0.25 | > 0.25 |

Performance budget recommendations

| Resource type | Budget | |---------------|--------| | Total page weight | < 1.5 MB | | JavaScript | < 300 KB (compressed) | | CSS | < 100 KB (compressed) | | Images | < 500 KB total above-fold | | Fonts | < 100 KB | | Third-party | < 200 KB |

Lighthouse score targets

| Category | Target score | |----------|--------------| | Performance | ≥ 90 | | Accessibility | 100 | | Best Practices | ≥ 95 | | SEO | ≥ 95 |

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
• web.dev Learn Performance
• Core Web Vitals
• WCAG 2.1 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.