Understanding Core Web Vitals

Google started using Core Web Vitals for search rankings in 2021. If your site is slow it can hurt your rankings.

What are Core Web Vitals

There are three metrics that measure user experience.

LCP (Largest Contentful Paint) measures loading. It tracks when the largest image or text appears. Should be under 2.5 seconds.

FID (First Input Delay) measures interactivity. The time between clicking something and the browser responding. Target under 100 milliseconds.

CLS (Cumulative Layout Shift) measures visual stability. How much stuff moves around while loading. You may have seen this when you try to click a button but an ad loads and shifts everything down.

Checking your scores

Use Lighthouse in Chrome DevTools. Open DevTools, go to Lighthouse tab, run an audit.

Common fixes

LCP issues usually come from large images. Compress images and use WebP format.

FID issues happen when JavaScript blocks the main thread. You can defer scripts that arent needed right away.

CLS issues usually come from images without dimensions. Set width and height on images so the browser knows how much space to reserve.

Learning more

Check out web.dev for detailed guides on improving each metric.