Core Web Vitals are the three performance metrics Google uses to evaluate page experience. Understanding them is the first step toward fixing the scores that affect your rankings.
Why Google Created Core Web Vitals
In 2021, Google formalized three specific metrics (Largest Contentful Paint, Cumulative Layout Shift, and Interaction to Next Paint) as official ranking signals under the umbrella of "Core Web Vitals." The decision reflected something the industry had known for years: fast, stable pages convert better, and Google's business depends on sending users to pages that deliver good experiences.
Before Core Web Vitals, site speed was measured by crude proxies like total load time. The new metrics are more nuanced. They measure real user perception rather than arbitrary file download timing. A site can load in 2 seconds but still fail Core Web Vitals if the visible content appears slowly or if elements shift around while the user is trying to click something.
LCP: Largest Contentful Paint
Largest Contentful Paint measures how long it takes for the main content of a page, usually a hero image or above-the-fold heading, to become visible to the user. Google's threshold is 2.5 seconds for a "Good" score. Anything above 4 seconds is rated "Poor."
The most common causes of slow LCP are unoptimized hero images (large JPEGs or PNGs that aren't served in modern formats like WebP), render-blocking scripts that delay everything on the page, and slow server response times. Improving LCP almost always starts with image optimization and eliminating third-party scripts that block rendering.
CLS: Cumulative Layout Shift
Cumulative Layout Shift measures visual stability, specifically, whether elements on the page unexpectedly jump around while the content is loading. If you've ever tapped a button on your phone only to have something load and push the button down at the last second, that's a high CLS experience. Google considers a score under 0.1 "Good."
CLS is typically caused by images or ads without defined dimensions (so the browser doesn't reserve space for them), web fonts that cause text to reflow when they load, or dynamically injected content that pushes other elements down. The fix usually involves adding width and height attributes to images, using font-display settings to prevent layout shifts, and reserving space for any dynamic content.
INP: Interaction to Next Paint
Interaction to Next Paint replaced the older First Input Delay metric in 2024. It measures how quickly a page responds to user interactions (clicks, taps, keyboard inputs) throughout the entire visit. A good INP score is under 200 milliseconds.
Poor INP is almost always caused by JavaScript that blocks the main thread: heavy scripts executing simultaneously, large React or Vue bundles, analytics libraries, tag managers, and ad scripts all competing for processing time. Improving INP requires auditing and reducing JavaScript execution, removing unused scripts, deferring non-critical code, and in some cases replacing heavy frontend frameworks with lighter alternatives.
How to Check Your Core Web Vitals
Google PageSpeed Insights (free) gives you both lab data and field data for any URL. Lab data comes from a simulated test; field data (when available) comes from real users visiting your site via Chrome. The field data matters more for SEO purposes.
Google Search Console provides aggregate Core Web Vitals reports under the "Experience" section, showing how your real pages are performing across mobile and desktop. If Search Console shows pages in the "Poor" or "Needs Improvement" buckets, those pages are likely being deprioritized in rankings relative to faster competitors.
Core Web Vitals are real ranking signals, not vanity metrics. LCP measures how fast your content appears, CLS measures how stable the layout is while loading, and INP measures how responsive the page is to user interaction. Improving all three improves both rankings and conversion rates.