What is Core Web Vitals?
Core Web Vitals are three Google-defined page-experience metrics that measure real-user loading speed, interactivity, and visual stability: Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). They became a Google ranking factor in 2021 and are reported in Google Search Console.
Source:web.dev — Core Web Vitals ↗
What to know in practice
- LCP target: under 2.5 seconds. Measures when the main content of a page becomes visible. Usually limited by hero-image weight or render-blocking JavaScript.
- INP target: under 200 milliseconds. Replaced First Input Delay (FID) in March 2024. Measures responsiveness to user input across the page's lifecycle.
- CLS target: under 0.1. Measures unexpected layout shifts during page load. Common causes: ads loading after content, web fonts without `font-display`, images without explicit width/height.
- Field data (Chrome User Experience Report) is what Google uses for ranking, NOT lab data (Lighthouse). PageSpeed Insights shows both — only field data matters for SEO.
Common misconception
Core Web Vitals have modest direct ranking impact — Google has said it's a tiebreaker, not a primary signal. The larger SEO impact is indirect: better Core Web Vitals reduce bounce rate, which improves engagement signals, which compounds to better rankings over time.