Core Web Vitals in Plain Language

Core Web Vitals sound like a technical formality. They are really three questions a visitor asks without thinking: has it loaded, can I use it, and did it move while I was looking at it.

LCP: has the main thing appeared

Largest Contentful Paint measures how long until the biggest element on screen, usually a hero image or headline, is visible. Aim for under 2.5 seconds. The fixes are rarely exotic: compress and correctly size that hero image, serve it in a modern format, stop loading it after three rounds of JavaScript, and make sure your server responds quickly on the first request.

INP: does it respond when I tap

Interaction to Next Paint replaced First Input Delay and measures the lag between a tap and something visibly happening. Long-running scripts are the usual cause, and third-party tags are the usual scripts. Auditing what you load, and deferring anything not needed for the first screen, moves this metric more than any code change.

CLS: did the page jump

Cumulative Layout Shift catches content that moves as things load, which is what makes people tap the wrong button. It is almost always images or ad slots without reserved dimensions, or a web font swapping in at a different size. Reserving space up front fixes most of it.

Measure with field data from real visitors rather than a lab score. A site can pass a test on a fast office connection and still fail for the customer on a phone in traffic.