Google's Core Web Vitals—Largest Contentful Paint, First Input Delay, and Cumulative Layout Shift—quantify user experience. These metrics affect search rankings and correlate with engagement. Systematic optimization requires understanding what each metric measures and targeted improvements.
Metric-Specific Optimization
LCP measures loading performance—optimize by preloading critical resources, using efficient image formats, and reducing server response times. FID measures interactivity—minimize JavaScript blocking the main thread. CLS measures visual stability—reserve space for dynamic content preventing layout shifts.
- Preload LCP images and critical fonts to start loading immediately
- Lazy load below-the-fold images to prioritize visible content
- Use next/image or similar for automatic image optimization
- Set explicit dimensions on images and embeds preventing layout shifts
- Code split JavaScript loading only what's needed for initial render
Measurement and Monitoring
Lab tools like Lighthouse provide controlled measurements. Real User Monitoring captures actual user experience across devices and networks. Track Core Web Vitals in production to catch regressions. Set performance budgets failing builds when metrics degrade.