Core Web Vitals
Definition
Core Web Vitals are Google's indicators measuring the real loading experience of your site: display speed, visual stability and responsiveness.Google measures what your visitors actually experience through three main indicators: LCP (Largest Contentful Paint) measures how long the main element of the page takes to display; CLS (Cumulative Layout Shift) measures visual stability, the content that jumps around during loading and makes you click the wrong thing; INP (Interaction to Next Paint) measures responsiveness to clicks.
These measures count twice. For your visitors first: every extra second of loading drives a share of them away, especially on mobile. Then for your visibility: Google includes these signals in its ranking criteria.
Good scores are not obtained with an optimisation plugin bolted on afterwards: they are built at design time. Images served in the right format and size, code without bloat, reserved dimensions to avoid layout jumps, lazy loading of whatever is not immediately visible.
It is a component of technical SEO, built into our developments by default. Speed is also one of the 5 principles of design that converts.
Test your site on PageSpeed Insights (free): it reports your Core Web Vitals measured on real users, not in a lab. Look at the mobile column above all.