Core Web Vitals

Core Web Vitals are metrics Google uses to measure the real experience of site visitors, with data collected from Chrome browsers. They are one of the ranking signals and, more importantly, they reflect whether visitors give up before seeing the page.

How it works

The three metrics are: LCP (Largest Contentful Paint), the time until the largest visible element appears, with a target below 2.5 s; INP (Interaction to Next Paint), the response time to clicks and taps, with a target below 200 ms; and CLS (Cumulative Layout Shift), how much the layout jumps while loading, with a target below 0.1. Heavy images, fonts and third-party scripts are the most common causes of poor scores.

Practical example

A manufacturer’s site had a 5.8 s mobile LCP because of a 4 MB hero photo and three chat and tracking scripts. With a responsive WebP image, a preloaded font and deferred scripts, LCP dropped to 1.9 s and mobile contact rate went up.

Common mistakes

• Measuring only on the office computer with fast internet.
• Installing several third-party plugins and widgets at the top of the page.
• Not reserving space for images and banners, which makes the layout jump.