What is Core Web Vitals?
Definition
Core Web Vitals are Google's three user-experience metrics — LCP (loading speed), INP (responsiveness) and CLS (visual stability) — measured on real visits. They're a confirmed ranking signal and a strong proxy for whether visitors stay or bounce.
LCP (Largest Contentful Paint) should be under 2.5s — how fast the main content appears. INP (Interaction to Next Paint) should be under 200ms — how quickly the page reacts to taps and clicks. CLS (Cumulative Layout Shift) should stay under 0.1 — how much the layout jumps around while loading.
Google grades these from Chrome's real-user data (CrUX), not lab tests, so a fast developer laptop means nothing if customers on mid-range phones over 4G have a slow experience. Common fixes: optimised images with fixed dimensions, less third-party JavaScript, font loading discipline and a CDN.
Example
An e-commerce site cuts LCP from 4.8s to 1.9s by compressing hero images to WebP and deferring its tag manager. Bounce rate drops, and pages stuck on position 8–10 move up as the site clears the "good" threshold.
Why it matters
Speed is the cheapest conversion lever you have — the same traffic converts measurably better on a fast site — and it's one of the few ranking factors entirely under your control.
PageSpeed Insights (pagespeed.web.dev) shows both lab scores and 28-day real-user data, and Search Console's Core Web Vitals report shows which URL groups pass or fail.
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