addyosmani/web-quality-skills
ShellAgent Skills for optimizing web quality based on Lighthouse and Core Web Vitals.
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 2.2 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 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
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 2.2 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
| 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.
- Fork the repository
- Create your skill in
skills/{skill-name}/SKILL.md - Keep SKILL.md under 500 lines (use
references/for details) - Include practical examples and patterns
- Submit a pull request
Resources
- Google Lighthouse Documentation
- web.dev Learn Performance
- Core Web Vitals
- WCAG 2.2 Guidelines
- Agent Skills Specification
License
MIT License - see LICENSE for details.
Built with insights from the Chrome DevTools team, web performance experts, and accessibility advocates to help developers create high-quality web experiences.