What Are Core Web Vitals?
Core Web Vitals are a set of real-world performance metrics Google uses as a ranking signal. As of 2024, the three metrics are LCP (Largest Contentful Paint), INP (Interaction to Next Paint), and CLS (Cumulative Layout Shift).
LCP — Target: Under 2.5 seconds
LCP measures how long the largest visible element takes to render. Common culprits: unoptimised hero images, render-blocking CSS, slow server response. Fix: use WebP images, preload the LCP element, and enable CDN caching.
INP — Target: Under 200ms
INP replaced FID in 2024 and measures responsiveness to all interactions, not just the first. Long JavaScript tasks are the primary cause. Fix: break up tasks over 50ms, defer non-critical JS, and use a web worker for heavy computation.
CLS — Target: Under 0.1
CLS measures how much the page visually shifts during load. The main causes are images without dimensions and late-loading ads or embeds. Fix: always set explicit width/height on images and reserve space for dynamic content.
Tools to Measure
- PageSpeed Insights — field + lab data
- Chrome DevTools Performance panel
- Google Search Console → Core Web Vitals report