TL;DR: Lighthouse = Google's site quality audit tool. Scores 0-100 on Performance, Accessibility, Best Practices, SEO. Above 90 = good. Open DevTools → Lighthouse tab to run.
4 Categories
1. Performance
Measures loading speed, Core Web Vitals.
- Optimize images (WebP, size).
- Minify CSS/JS.
- Lazy loading.
- Reduce unused code.
- CDN.
2. Accessibility
A11y compliance.
- Alt text on images.
- Color contrast.
- ARIA labels.
- Keyboard navigation.
- Semantic HTML.
3. Best Practices
Web development best practices.
- HTTPS.
- No console errors.
- Modern image formats.
- No deprecated APIs.
4. SEO
Basic SEO health.
- Title tag.
- Meta description.
- Viewport meta.
- Crawlable.
- Valid robots.txt.
How to Run
- Chrome DevTools (F12).
- Lighthouse tab.
- Select device (Mobile recommended).
- Select categories.
- Generate report.
Target Scores
- Performance: 90+ (hard).
- Accessibility: 95+.
- Best Practices: 100.
- SEO: 100.
Common Low Scorers
- Performance. most sites 30-70. Need work.
- Accessibility. often 70-85.
- SEO. easy to 90+ if basics covered.