Core Web Vitals are Google's three metrics for real-world page experience: Largest Contentful Paint (LCP, loading speed), Cumulative Layout Shift (CLS, visual stability) and Interaction to Next Paint (INP, responsiveness). Google uses them as a ranking signal.
This free checker measures your site against Google's official thresholds and shows exactly which elements are dragging each metric down — so you know what to fix first.
Google distilled 'page experience' into three measurable metrics. Largest Contentful Paint (LCP) is how long the biggest thing on screen — usually your hero image or headline — takes to appear. Cumulative Layout Shift (CLS) measures how much the page jumps around while loading, like when a late image pushes text down. Interaction to Next Paint (INP) measures how quickly the page reacts when someone taps or clicks.
Together they answer three questions a real visitor cares about: did it load quickly, did it stay still, and did it respond fast?
Poor LCP usually comes from a large unoptimized hero image, a slow server response, or render-blocking CSS delaying the first paint. Poor CLS comes from images and ads without reserved space, or web fonts that swap and reflow text. Poor INP comes from heavy JavaScript that keeps the main thread busy so taps feel laggy.
This checker measures your real field data and then inspects the page to point at the exact element or script behind each failing metric — so you fix the cause, not the symptom.
For LCP: compress and preload your hero image, serve WebP/AVIF, and speed up your server with caching. For CLS: set width and height on every image, and reserve space for ads and embeds. For INP: defer or split heavy JavaScript and remove unused scripts.
The full report ranks these fixes by impact so you can pass the vitals with the least effort — and you can re-test any time to watch the scores improve.
LCP under 2.5s, CLS under 0.1, and INP under 200ms. This checker shows where your pages stand against these targets.
In March 2024, Google replaced First Input Delay (FID) with Interaction to Next Paint (INP) as a Core Web Vital. This tool reports INP.
Mobile devices are slower and on weaker networks, so mobile vitals are usually worse — and Google primarily uses mobile for ranking.
Set explicit width/height on images and reserve space for ads/embeds so content doesn't jump. The report pinpoints the shifting elements.
Lab data is a single simulated test; field data (CrUX) is aggregated from real Chrome users over 28 days. Google ranks on field data, which is why this checker prioritizes it.
Yes — they're part of Google's page-experience signals. They rarely outweigh great content, but between two similar pages, the faster, more stable one wins.