Core Web Vitals, Explained Without Jargon

Google grades every page on three user-experience numbers. Here's what they mean and what actually moves them.

LCP — Largest Contentful Paint

How long until the biggest thing on screen (usually the hero image or headline) appears. Good: under 2.5 s. Moved by: faster server response, image compression, and preloading the hero image.

INP — Interaction to Next Paint

How quickly the page reacts when users tap or type. Good: under 200 ms. Moved by: less JavaScript, fewer third-party scripts, and breaking up long tasks.

CLS — Cumulative Layout Shift

How much the page jumps around while loading. Good: under 0.1. Moved by: giving images and ads explicit dimensions and never injecting content above what's already rendered.

Where to see your numbers

PageSpeed Insights shows two kinds of data: real-user field data (what Google actually measured from Chrome users, when your site has enough traffic) and lab data from a simulated device. Field data is what counts for rankings; lab data is what you debug with.

Once you can read the numbers, run the 10-minute diagnosis to fix them in the right order.