Largest Contentful Paint asks when the main thing appeared. Interaction to Next Paint asks how long the page took to respond when someone tried to use it. Cumulative Layout Shift asks how much the content moved under them while it loaded. Together they approximate the experience of a page well enough to be worth optimising directly.
The distinction that matters is field versus lab. A lab tool scores one run on one machine on a fast connection; the field data is what actual visitors experienced on the phones and networks they actually have, at the 75th percentile, and the two regularly disagree. A perfect lab score alongside failing field data usually means the audience is on worse hardware than the person running the test.
Related terms
LCP (Largest Contentful Paint)
The moment the biggest piece of content in the viewport finishes rendering — in practice, when the page looks loaded.
Hydration
The step where JavaScript takes over server-rendered HTML in the browser and makes it interactive.
Static generation (SSG)
Rendering pages to HTML at build time, so a request is answered by handing over a file instead of running code.
The bench this belongs to
Web performanceA rebuild that loads on a phone on mobile data, in the country your customers are actually in. Core Web Vitals are the measurement, revenue is the point.
