Performance Metrics Tool

Core Web Vitals, explained

Core Web Vitals are the three user-experience metrics Google uses as a ranking signal: LCP (Largest Contentful Paint) measures loading — how fast the main content appears; INP (Interaction to Next Paint) measures responsiveness — how quickly the page reacts to input; and CLS (Cumulative Layout Shift) measures visual stability — how much the layout jumps as it loads.

Google considers a page 'good' when LCP is under 2.5s, INP under 200ms and CLS under 0.1, measured on real users (field data) at the 75th percentile. Lab tools like Lighthouse estimate these, but field data from the Chrome UX Report is what actually influences rankings.

How to use the performance tool

Enter a URL to get a Lighthouse-style breakdown of LCP, INP and CLS plus the specific opportunities behind each score — render-blocking resources, unused JavaScript, oversized images, missing image dimensions and more. Each finding maps to a concrete fix.

The fastest ways to improve Core Web Vitals

For LCP: compress and correctly size your hero image (or preload it), self-host fonts with font-display:swap, and cut render-blocking CSS/JS. For INP: reduce and split large JavaScript bundles so the main thread is not blocked. For CLS: always set width and height on images and reserve space for embeds and ads so nothing shifts as the page loads.

Frequently asked questions

Is lab data the same as what Google ranks on?

No. Google ranks on field data (real Chrome users). Lab tools estimate it, so always confirm improvements in field data before declaring victory.

What is a good LCP?

Under 2.5 seconds at the 75th percentile of real users. Between 2.5s and 4s needs improvement; over 4s is poor.

Do Core Web Vitals really affect rankings?

They are a real but modest ranking signal, and they strongly affect conversion. Fast, stable pages keep more of the traffic you already earn.