Core Web Vitals are three Google metrics that measure real-world user experience on web pages: LCP (Largest Contentful Paint) measures loading speed — how quickly the main content appears; INP (Interaction to Next Paint) measures responsiveness — how fast the page reacts to user interactions; CLS (Cumulative Layout Shift) measures visual stability — whether page elements move unexpectedly while loading. Google uses Core Web Vitals as ranking signals. Pages that pass all three thresholds (LCP under 2.5s, INP under 200ms, CLS under 0.1) receive a ranking advantage over pages that fail.
Core Web Vitals replaced the older Page Speed metrics as Google's primary user experience ranking signal in 2021. The three metrics were chosen because they measure the aspects of page experience that most directly correlate with user frustration and abandonment — slow loading, unresponsive interactivity, and content that jumps around while the page loads. Passing all three is now a baseline technical requirement for competitive search performance.
How to improve each Core Web Vital
- LCP (target: under 2.5 seconds) — optimise hero images (WebP/AVIF format, preload hint), minimise render-blocking CSS and JavaScript, use a CDN, enable server-side caching
- INP (target: under 200ms) — reduce JavaScript execution time, defer non-critical scripts, use web workers for heavy computation, avoid long main-thread tasks
- CLS (target: under 0.1) — set explicit dimensions on all images and videos, reserve space for late-loading ads and embeds, avoid injecting content above existing content, preload custom fonts
- All metrics: use a CDN for static assets, enable Brotli/gzip compression, implement lazy loading for below-fold images
Google PageSpeed Insights (free, at pagespeed.web.dev) provides field data (real user measurements) and lab data (simulated) for any URL. Google Search Console shows Core Web Vitals data across all pages of a verified site. Chrome's Lighthouse audit tool provides lab data in the browser DevTools. CrUX (Chrome User Experience Report) provides field data aggregated from real Chrome users. Field data is more important than lab data for ranking purposes — Google uses real user experience data, not simulated tests.
Google's Core Web Vitals are a tiebreaker ranking signal rather than a dominant factor — all else being equal, a page passing Core Web Vitals will rank above a failing page. For highly competitive keywords where all other factors are similar between competing pages, Core Web Vitals can be decisive. For less competitive keywords, content quality remains more important than Core Web Vitals performance. However, slow-loading pages have always had higher bounce rates, which indirectly affects all engagement metrics that Google uses as quality signals.