Lighthouse Score Explained
Understanding Performance, Accessibility, Best Practices & SEO
Learn how Lighthouse calculates scores, what each metric means, and how to achieve 90+ scores across all categories.
Test Your Lighthouse ScoreWhat is Lighthouse?
Lighthouse is Google's open-source tool for auditing web page quality. It measures Performance, Accessibility, Best Practices, SEO, and PWA readiness.
Performance Score (0-100)
Performance score is a weighted average of metric scores. Higher weights mean more impact on overall score.
Accessibility Score (0-100)
Measures how accessible your site is to users with disabilities. Based on automated WCAG 2.1 checks.
Common Issues
- •Missing alt text on images
- •Insufficient color contrast (< 4.5:1 ratio)
- •Missing form labels
- •Improper heading hierarchy (h1 → h3)
- •Links without descriptive text
- •Missing ARIA labels on interactive elements
Quick Fixes
- Add alt="description" to all images
- Use contrast checker tool (4.5:1 minimum)
- Wrap inputs with <label> elements
- Use proper heading order (h1, h2, h3)
- Descriptive link text (not "click here")
- Add aria-label to icon-only buttons
Best Practices Score (0-100)
Measures security, modern web standards, and general code quality.
HTTPS Required
All pages must use HTTPS (SSL certificate)
No Browser Errors
Console errors logged during page load penalize score
Modern Image Formats
Use WebP or AVIF instead of JPEG/PNG
Deprecated APIs
Avoid deprecated JavaScript APIs and libraries
Secure Connections
No mixed content (HTTP resources on HTTPS pages)
SEO Score (0-100)
Measures basic SEO best practices that help search engines understand and rank your content.
Meta Description
150-160 characters summarizing page content
Title Tag
Unique, descriptive, under 60 characters
Mobile Friendly
Proper viewport meta tag, responsive design
Crawlable Links
Use <a href> not JavaScript-only navigation
Structured Data
Schema.org markup for rich results
Robots.txt
Valid robots.txt, no blocked resources
How to Achieve 90+ on All Categories
Performance (90+)
- ✓ Optimize images (WebP, lazy loading)
- ✓ Use CDN for static assets
- ✓ Eliminate render-blocking resources
- ✓ Minimize JavaScript execution time
- ✓ Enable browser caching
Accessibility (90+)
- ✓ Add alt text to all images
- ✓ Ensure 4.5:1 color contrast
- ✓ Label all form inputs
- ✓ Use proper heading hierarchy
- ✓ Keyboard navigation support
Best Practices (90+)
- ✓ Use HTTPS everywhere
- ✓ Fix all console errors
- ✓ Use modern image formats
- ✓ Avoid deprecated APIs
- ✓ No mixed content warnings
SEO (90+)
- ✓ Unique meta descriptions
- ✓ Descriptive title tags
- ✓ Mobile-friendly design
- ✓ Valid structured data
- ✓ Proper canonical URLs
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