Core Web Vitals
TL;DR
Google's set of user experience metrics — LCP, CLS, and INP — used as ranking signals measuring loading speed, visual stability, and interactivity.
Core Web Vitals (CWV) are a set of standardised, field-measured web performance metrics defined by Google that quantify real-world user experience. Since 2021, they have been official Google ranking factors under the Page Experience update.
The three Core Web Vitals are: Largest Contentful Paint (LCP) — measures loading performance; good LCP is under 2.5 seconds. Cumulative Layout Shift (CLS) — measures visual stability (how much page elements unexpectedly shift during load); good CLS is under 0.1. Interaction to Next Paint (INP) — replaced First Input Delay in 2024 and measures overall responsiveness; good INP is under 200ms.
Improving Core Web Vitals typically involves: optimising image delivery (WebP format, lazy loading, next/image), reducing render-blocking resources, implementing server-side rendering or static generation, eliminating layout shifts from ads or embeds, and minimising JavaScript main-thread blocking. Strong CWV scores correlate with lower bounce rates, higher conversions, and improved organic rankings.
Examples in Practice
LCP < 2.5s means your largest image or text block loads in under 2.5 seconds. CLS < 0.1 means buttons and images don't shift around as the page loads.