Core Web Vitals

Core Web Vitals are a set of metrics defined by Google to measure real-world user experience on the web. They focus on three aspects of page quality: loading speed, interactivity, and visual stability. Since May 2021, these metrics have been official Google ranking signals, making them directly relevant to SEO performance.

The three metrics are Largest Contentful Paint (LCP), which measures how long the main content takes to load; Interaction to Next Paint (INP), which measures responsiveness to user input across the entire page lifecycle; and Cumulative Layout Shift (CLS), which measures how much the layout jumps around as elements load. Google publishes specific thresholds for each: LCP under 2.5 seconds, INP under 200 milliseconds, and CLS under 0.1 are considered good.

Improving Core Web Vitals typically involves a mix of technical changes. LCP improvement often means better server response times, optimized images, and removing render-blocking resources. CLS problems usually come from images without explicit dimensions, dynamically injected content, or web fonts that cause layout shifts before they load. INP issues often trace back to heavy JavaScript execution on the main thread blocking user input from being processed quickly.

Measuring these metrics requires real user data, not just lab tests. Google provides field data through PageSpeed Insights and Search Console, collected from real Chrome users via the Chrome User Experience Report. Lab tools like Lighthouse give useful approximations but do not perfectly match field conditions. Teams serious about performance should monitor both.