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.
In depth
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.
Source: web.dev: Core Web Vitals
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