Core Web VitalsCWV

What are the three Core Web Vitals?#

The three Core Web Vitals are Largest Contentful Paint (LCP), which measures loading; Interaction to Next Paint (INP), which measures responsiveness; and Cumulative Layout Shift (CLS), which measures visual stability — each judged at the 75th percentile of real Chrome users’ page loads, mobile and desktop separately.

INP replaced First Input Delay as a Core Web Vital on 12 March 2024, so any audit, plugin or agency report still quoting FID is out of date. A page passes only when all three metrics are good at the 75th percentile: up to a quarter of visits can be slower and the page still passes, but one poor metric fails it.

The data comes from the Chrome UX Report (CrUX), which records real visits from Chrome users — field data, not a lab simulation. That’s why the metrics reward what visitors actually experience on their own devices and connections, and why a fast developer laptop proves little.

Do Core Web Vitals affect rankings?#

Core Web Vitals do affect rankings — Google says they “are used by our ranking systems” — but modestly: Google also says it shows the most relevant content even when page experience is sub-par, and that chasing a perfect score just for SEO “may not be the best use of your time.”

• Used in ranking

  Official

  Google’s page experience FAQ: “Core Web Vitals are used by our ranking systems.” Other page experience aspects “don’t directly help your website rank higher.”

• Relevance comes first

  Official

  Google shows the most relevant content even if the experience is poor; a great experience helps most when many pages are equally helpful.

• Mostly page-level

  Official

  Google’s core ranking systems “generally evaluate content on a page-specific basis,” though it also has “some site-wide assessments.”

• Small sites may have no field data

  Official

  Search Console’s report needs a minimum amount of real-user data. Quiet URLs are grouped with similar pages or rolled up to the whole origin, and some are left out entirely.

How do you measure Core Web Vitals?#

Measure Core Web Vitals with field data from real Chrome users — Search Console’s Core Web Vitals report and PageSpeed Insights both draw on the Chrome UX Report — and use lab tools like Lighthouse only to debug, because a lab test has no real user and cannot measure INP.

// Send real-user Core Web Vitals to your own analytics endpoint
import { onCLS, onINP, onLCP } from "web-vitals";
 
function send(metric) {
  navigator.sendBeacon("/analytics", JSON.stringify({
    name: metric.name,     // "LCP" | "INP" | "CLS"
    value: metric.value,
    rating: metric.rating, // "good" | "needs-improvement" | "poor"
    page: location.pathname,
  }));
}
 
onCLS(send);
onINP(send);
onLCP(send);

Search Console grades each group of URLs by its slowest metric and reports the last 28 days of data, and its fix validation runs a 28-day monitoring session. Expect a month between shipping a fix and seeing it confirmed in Search Console.

Do Core Web Vitals matter for AI search?#

Core Web Vitals matter to AI search indirectly: Google’s AI Overviews and AI Mode rest on the same ranking systems that use them, but AI crawlers never click, scroll or watch the layout, so what they feel is server speed and page weight.

Google AI Overviews & AI ModeHelps

AI Overviews and AI Mode are grounded in core ranking, which uses Core Web Vitals. Google’s AI optimization guide lists “a good page experience” — including reducing latency — among the technical basics.

Server response timeHelps

Not a Core Web Vital, but the part of speed a bot experiences. Live fetchers such as ChatGPT-User, Claude-User and Perplexity-User retrieve pages while the user waits — see AI crawlers — and slow responses also lower how much Google crawls, as covered under crawl budget.

Fast first paintHelps

SE Ranking found pages with a first contentful paint under 0.4 seconds averaged 6.7 ChatGPT citations, against 2.1 for pages slower than 1.13 seconds. A correlation, not proof of cause.

Page weightRequired

Googlebot reads only the first 2 MB of a page’s HTML, and Brave’s discovery fetches — which feed Claude’s search provider — refuse pages over 2 MB and time out after 10 seconds.

INP and CLS, for AI crawlersNo effect

Crawlers don’t tap, type or look at the layout, so these can’t change what a bot reads. They still feed Google’s rankings, and through them its AI features.

Server-side rendering often helps both audiences at once: the HTML arrives complete, the largest element can paint without waiting for a script bundle, and non-rendering bots get the full text in a single fetch.

Common mistakes with Core Web Vitals#

The most common Core Web Vitals mistakes are optimizing a Lighthouse lab score instead of field data, chasing perfection on pages already rated good, still reporting First Input Delay after INP replaced it, and speeding up the homepage while the templates that earn traffic stay slow.

Related terms#

• SSRTechnical SEOServer-side renderingThe practice of generating a page’s full HTML on the server before sending it, so crawlers that don’t run JavaScript — which includes most AI crawlers — can read the content in the first response.Read the entry
• Technical SEOCrawl budgetThe number of URLs a search engine is willing and able to crawl on a site in a given period, set by how much load the server can take and how much the engine wants the content — a real constraint mainly for large or fast-changing sites.Read the entry
• SEOAI search & GEOSearch engine optimizationThe practice of improving a website’s content, technical setup and authority so search engines crawl, index and rank it for relevant queries — and because most AI answer engines retrieve their sources from a search index, it is also the foundation of AI visibility.Read the entry
• GSCMeasurementGoogle Search ConsoleGoogle’s free tool for site owners that reports how a site performs in Google Search — queries, impressions, clicks, position and indexing — and since 2026 it also reports impressions in Google’s generative AI features and lets owners opt out of them.Read the entry
• AI search & GEOAI OverviewsAI-generated summaries shown at the top of some Google search results, written by a Gemini model from pages in Google’s search index and linked to their sources — so they are won through ordinary Google eligibility, not a separate submission or special markup.Read the entry