Core Web Vitals

Core Web Vitals are three measurements Google uses to describe how a page behaves for a person loading it in a browser: how quickly the main content appears, how promptly the page responds to input, and how much the layout jumps around while it loads. They are part of Google’s page experience signals for Search.

The three metrics

Largest Contentful Paint measures loading: the time until the biggest visible element has rendered, with 2.5 seconds or less counted as good. Interaction to Next Paint measures responsiveness: the delay between a tap or click and the next screen update, good under 200 milliseconds. Cumulative Layout Shift measures visual stability: how far content moves unexpectedly, good below 0.1. The thresholds are on Google’s Core Web Vitals page, which also says the metrics align with what its ranking systems reward and points to the Core Web Vitals report in Search Console for a site’s own readings.

Where a crawler differs from a browser

All three metrics describe a browser session: a screen, a person, a script running. An AI crawler fetching a page to answer a question is none of those. It makes an HTTP request, receives HTML, and reads it; many fetchers do not execute JavaScript, so there is no rendering to be slow and no layout to shift. This site’s audit of 9,483 small-business sites used a crawler of that kind and found 3.0% of sites rendered their content only in JavaScript, which to such a fetcher is an empty page. That failure is invisible to Core Web Vitals, which would score the same site well once the script had run.

One question

Do Core Web Vitals affect whether an AI assistant cites a page?

Indirectly for Google, and barely for the rest. Google says a page needs to be indexed and eligible for a snippet to be a supporting link in AI Overviews or AI Mode, with no separate requirements, so the vitals matter there to the extent they matter to indexing and ranking. Other assistants fetch the page over HTTP and read the served text; what decides citation is whether the text arrived and whether it holds an answer, not how the page painted in a browser.

Sources

Metric definitions and thresholds: Google’s Core Web Vitals page. Requirements for AI features: Google’s documentation on AI features in Search. The 3.0% figure is this site’s own; sample drawn per metro and trade, percentages describe the sample.