Core Web Vitals Checker

Core Web Vitals are three metrics Google uses to measure real-user page experience: LCP (Largest Contentful Paint — load speed of the main content), INP (Interaction to Next Paint — how fast the page responds to clicks), and CLS (Cumulative Layout Shift — how much the layout jumps while loading). Together they measure whether your page actually feels fast and stable. Test in PageSpeed Insights or our Core Web Vitals Checker; field data from real Chrome users is what Google actually uses for ranking.

Google's thresholds: 2.5 seconds or less is good, 2.5 to 4 seconds needs improvement, above 4 seconds is poor. LCP measures when the largest visible element — usually a hero image or main heading — finishes loading. Mobile is harder because of slower connections; desktop usually beats mobile by 1 to 2 seconds. E-commerce homepages with big banners often struggle here. The biggest wins come from compressing the LCP image, preloading it, and trimming render-blocking CSS.

INP, Interaction to Next Paint, replaced FID in March 2024. It measures the longest delay between a user interaction (click, tap, key press) and the next visual update on the page, across all interactions in a session. Good is 200 ms or less; needs improvement 200 to 500 ms; poor above 500 ms. INP is harder to fix than FID because it captures real interaction patterns, not just the first one. Heavy JavaScript, unoptimized event handlers, and main-thread blocking are the usual culprits.

Cumulative Layout Shift thresholds: 0.1 or less is good, 0.1 to 0.25 needs improvement, above 0.25 is poor. CLS measures how much visible content jumps around while the page loads — banners pushing the article down, ads appearing late, fonts swapping in. Common fixes: set width and height attributes on images and embeds, reserve space for ad slots, and use 'font-display: optional' for web fonts. CLS is usually the easiest of the three to bring into the green zone.

Yes, since the page experience update in 2021. The effect is real but small — Google calls it a tiebreaker between pages of similar quality. So fixing Core Web Vitals won't move a thin page from page 5 to page 1, but among comparable competitors it can shift you up a few spots. The bigger gain is usually conversion: faster pages reduce bounce and lift conversion rate by 5% to 15% in most tests. Worth fixing for the conversion benefit alone.

Lab data comes from a controlled test environment — same device, same network, run on demand. It's reproducible and good for debugging specific issues. Field data comes from real Chrome users (CrUX dataset) over the past 28 days. It's what Google actually uses for the page experience signal. The catch: lab can show good numbers while field shows poor, because real users have slower phones and worse connections than the lab simulation. Always treat field data as the source of truth and use lab to diagnose.

Highest-impact levers in order: compress and preload the LCP image, reduce JavaScript bundle size and defer what's non-critical, set explicit dimensions on all images and embeds, use a CDN, switch to modern image formats (WebP or AVIF), and enable HTTP/2 or HTTP/3. Track the field data in Search Console's Core Web Vitals report — it updates every few days based on real Chrome users. Most sites can move from poor to good within 4 to 8 weeks of focused work.