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Core Web Vitals are three performance metrics Google uses as ranking signals. LCP (Largest Contentful Paint) measures how long the main content takes to load from the moment the page starts loading. INP (Interaction to Next Paint) measures how quickly the page responds to user input. CLS (Cumulative Layout Shift) measures visual stability during load, meaning how much content moves around unexpectedly.
Google considers these signals as part of the Page Experience ranking factors. A page scoring well on all three has a measurable advantage over a comparable page that does not, particularly on mobile.
| Metric | Good | Needs improvement | Poor | What it measures |
|---|---|---|---|---|
| LCP | < 2.5s | 2.5-4s | > 4s | Time for largest visible content to load |
| INP | < 200ms | 200-500ms | > 500ms | Response time to user interactions |
| CLS | < 0.1 | 0.1-0.25 | > 0.25 | Amount of unexpected layout shift |
Google confirmed Core Web Vitals as ranking factors in 2021 and updated INP as the interactivity metric in 2024. The effect is most noticeable on competitive queries where pages are otherwise similar in quality. A page that scores well tends to be favoured, all else being equal.
The larger effect of slow pages is on user behaviour. A page that takes more than three seconds to load on mobile loses a significant portion of its visitors before they have seen any content. That translates directly into lower engagement and worse conversion rates.
LCP (Largest Contentful Paint) is the time for the page's main visible element to finish loading. Aim for under 2.5 seconds. INP (Interaction to Next Paint) measures how fast the page reacts to clicks and taps. Aim for under 200ms. CLS (Cumulative Layout Shift) is a score for how much the layout shifts unexpectedly as the page loads. Aim for under 0.1.
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The tool returns both. Lab data (Lighthouse) measures performance in a controlled environment using a simulated device and connection. Field data (Chrome User Experience Report) reflects real visits from actual users. Lab data is useful for diagnosing specific issues. Field data shows what real users actually experience.
Core Web Vitals measure specific technical events, not the overall perception of speed. A page can score well on LCP while still feeling slow if there is a lot of JavaScript executing after load, if fonts swap in late, or if interactive elements take time to become functional. These issues do not always show up in Core Web Vitals scores but do affect how the page feels to use.
Page speed does not directly determine whether an AI system cites your content. But it does affect whether crawlers can fully index your pages. A slow page with a high time-to-first-byte may be crawled less thoroughly. Pages that perform poorly on technical signals tend to perform poorly across all quality signals that AI search systems consider.