Core Web Vitals

Core Web Vitals are three metrics Google uses to measure the real-world user experience of a web page: Largest Contentful Paint (LCP) for loading, Interaction to Next Paint (INP) for responsiveness, and Cumulative Layout Shift (CLS) for visual stability. They are measured from real Chrome users and form part of the page experience signals that, in Google's words, align with what its core ranking systems seek to reward.

The thresholds for a 'good' experience, unchanged since INP replaced First Input Delay (FID) as the responsiveness metric in March 2024, are:

• LCP of 2.5 seconds or less: the time until the largest visible image or text block renders.
• INP of 200 milliseconds or less: the delay between a user's click, tap or key press and the next visual update, measured across the whole visit rather than only the first interaction.
• CLS of 0.1 or less: how much visible content moves unexpectedly while the page loads and is used.

Google assesses each metric at the 75th percentile of page loads, separately for mobile and desktop, and a page passes only if all three are good. The field data comes from the Chrome User Experience Report (CrUX) and feeds PageSpeed Insights and the Core Web Vitals report in Google Search Console. Lab tools such as Lighthouse can measure LCP and CLS but not INP, because there is no real user interacting; Total Blocking Time is the usual lab stand-in.

Most of the web still falls short. In the CrUX dataset for September 2026, published October 13, 2026 and covering about 18.4 million origins, 55.9% of origins had good Core Web Vitals overall: 68.3% had good LCP, 81.7% good CLS and 85.4% good INP. The same release added experimental versions of all three metrics that count soft navigations, the in-app page changes of single-page applications, which raise pass rates for those sites. Chrome is targeting May 2027 for these to leave experimental status, and says Search Console will switch to the new data once they do; until then, stable scores are unchanged.

For SEO, Core Web Vitals are a real but modest factor: they will not lift weak content past stronger pages, but poor scores can hold back pages that are otherwise competitive, and they directly affect bounce and conversion. Common fixes are compressing and correctly sizing images, preloading the main image, reducing render-blocking CSS and JavaScript, and improving server response time for LCP; breaking up long JavaScript tasks and deferring third-party scripts for INP; and setting width and height on images, embeds and ad slots for CLS.

For AI search, the link is indirect. Core Web Vitals measure what human visitors in Chrome experience, and there is no public evidence that ChatGPT, Perplexity or Claude use them to choose sources. Google's guidance for AI Overviews and AI Mode lists a good page experience among the SEO fundamentals that remain worthwhile, and the underlying speed work helps crawlers too: Google's crawl budget documentation says faster, stable server responses let it crawl more, and many AI crawlers fetch raw HTML without running JavaScript, so content that appears only after heavy client-side rendering may be missed. Fast server-rendered pages serve both audiences. The free AI SEO audit checks server response time and crawler access, which complements field data from Chrome. See the official Core Web Vitals guide on web.dev for measurement details.