Free Core Web Vitals Test: LCP, INP, CLS

Core Web Vitals are Google's official metrics for measuring page experience: LCP (loading performance), FID/INP (interactivity) and CLS (visual stability). Since 2021, they have been direct ranking factors in Google's algorithm. Sites with good Core Web Vitals scores get a ranking boost, while poor scores can hurt your visibility in search results. They are essential for both SEO and user experience.

Mobile and desktop metrics often differ significantly because of network speeds, device capabilities and rendering differences. Google uses mobile-first indexing, which means your mobile performance matters more for rankings. Mobile devices usually have slower network connections and less processing power, so LCP and INP scores are generally worse on mobile. You should prioritize mobile optimization first.

INP (Interaction to Next Paint) replaced FID (First Input Delay) as a Core Web Vital in March 2024. While FID only measured the delay of the first interaction, INP measures the responsiveness of all user interactions throughout the page lifecycle. This gives a more complete view of interactivity. A good INP is under 200 ms, needs improvement between 200-500 ms, and is poor above 500 ms.

To improve LCP: 1) Optimize and compress images using WebP/AVIF formats, 2) Use a CDN to reduce server response times, 3) Lazy-load images below the fold, 4) Preload critical resources such as fonts and hero images, 5) Minimize render-blocking JavaScript and CSS, 6) Upgrade to better hosting with faster servers, and 7) Enable text compression (Gzip/Brotli).

Use our tool to reduce image weight and improve LCP, and our HTML/CSS/JS minifier to quickly eliminate render-blocking resources.

CLS measures unexpected layout shifts. Common causes include: 1) Images without width/height attributes, 2) Ads or embeds that load dynamically, 3) Web fonts causing FOIT/FOUT (Flash of Invisible/Unstyled Text), 4) Animations that push content around, and 5) Late-loading content that shifts existing elements. Fix this by setting explicit dimensions, reserving space for dynamic content and using font-display: swap.

Check Core Web Vitals weekly for critical pages (homepage, main landing pages, product pages) and monthly for other pages. Always test after major updates, design changes or new feature releases. Use this tool alongside the Core Web Vitals report in Google Search Console and PageSpeed Insights to monitor trends and catch problems before they affect rankings.

A good overall score means passing all three core metrics: LCP under 2.5 seconds, FID under 100 ms (or INP under 200 ms) and CLS under 0.1. Google requires 75% of page visits to meet these thresholds for a “good” rating. Aim for: TTFB under 800 ms, FCP under 1.8 s, and every Core Web Vital in the “good” range on both mobile and desktop.