Glossaire · SEO

Core Web Vitals

Core Web Vitals are a set of three metrics defined by Google to measure the quality of a web page's user experience: LCP (Largest Contentful Paint), which evaluates how fast the main content loads; INP (Interaction to Next Paint), which measures responsiveness to interactions; and CLS (Cumulative Layout Shift), which quantifies the visual stability of the layout. Each metric has a threshold rated as good, needs improvement, or poor. Part of the Page Experience ranking factor, Core Web Vitals influence Google organic rankings and reflect how visitors actually perceive a site. They rely on field data collected through the CrUX (Chrome User Experience Report) and have become an essential standard for evaluating a site's technical performance in 2026.

Core Web Vitals have become the common language for discussing web performance. Rather than abstract technical numbers, they capture what a visitor feels: does the page appear quickly, does it respond to clicks, does it stay stable under the fingers?

How it works

Google measures Core Web Vitals in two complementary ways. Field data comes from the Chrome User Experience Report, which aggregates real visits from Chrome users who opted into data sharing. This is the data that counts for ranking. Lab data, produced by tools like Lighthouse or PageSpeed Insights, simulates a load to diagnose and reproduce issues before deployment.

Each metric is scored at the 75th percentile: to earn a good rating, at least 75% of loads must meet the threshold. This is demanding, because it includes slow connections and low-powered devices.

The three metrics

LCP: time to display the largest visible element (hero image, text block). Target: under 2.5s.
INP: latency between an interaction and the page's visual response. Target: under 200ms. INP replaced FID in March 2024.
CLS: the magnitude of unexpected visual shifts during loading. Target: under 0.1.

Why it matters

A fast, stable page reduces bounce rate, increases time on site, and improves the conversion rate. For SEO, Core Web Vitals reinforce a technically healthy site, a baseline condition for content to rank durably.

A retenir

Core Web Vitals measure real visitor experience, not a lab score. Optimize field CrUX data first.

At LUWIZ, we treat Core Web Vitals as a foundation: a slow site sabotages every other SEO and GEO effort, because neither users nor crawlers will wait.

FAQ

Questions fréquentes

Yes. They are part of the Page Experience signal used by Google. Their weight remains moderate compared to content relevance, but they break ties between pages of equal quality and improve the real user experience.

An LCP below 2.5 seconds, an INP below 200 milliseconds, and a CLS below 0.1 are considered good by Google, across 75% of page loads.

Pour aller plus loin