Glossary
Core Web Vitals
Core Web Vitals are Google's three user-experience metrics — Largest Contentful Paint, Interaction to Next Paint, and Cumulative Layout Shift — used as a ranking signal in search.
Core Web Vitals are three measurable metrics Google uses to score the user experience of a webpage. They're part of the broader page-experience signals Google factors into search rankings.
LCP (Largest Contentful Paint) — when the largest visible element renders. Good: ≤2.5s. INP (Interaction to Next Paint) — how responsive the page is to user input. Good: ≤200ms. CLS (Cumulative Layout Shift) — how much the layout jumps around as it loads. Good: ≤0.1.
Core Web Vitals are a ranking factor in Google's page-experience signals. Sites that fail Core Web Vitals can lose rankings to faster competitors even when content quality is identical. The gap matters most in close ranking competitions — a site at position 6 and another at position 5 with the same content quality will see Core Web Vitals tip the comparison.
Measurement: Lighthouse (Chrome DevTools) for lab-based testing, PageSpeed Insights for both lab and field data, the CrUX (Chrome User Experience Report) dataset for real-user metrics aggregated across 28 days. Field data is what Google actually uses for ranking; lab data is what developers use for debugging.
Common Core Web Vitals failures: oversized hero images (LCP), heavy JavaScript bundles blocking interaction (INP), late-loading fonts shifting text (CLS), and ads / embeds that load after layout (CLS). Most are addressable with the same techniques: image optimization, code splitting, font-display: swap, and reserving space for late-loading content.
Example
A site with a 4-second LCP from a heavy hero video can lose top-3 rankings to a competitor whose LCP is 1.2s — same content, different infrastructure. Compressing the video, using next/image with priority, and lazy-loading below-fold assets often gets the LCP back under 2s.