Core Web Vitals get mentioned constantly in SEO advice, usually without much explanation of what they actually measure. There are three, and each one maps to something a real visitor would actually notice.
LCP — how fast the main content shows up
Largest Contentful Paint measures how long it takes for the biggest visible element — usually a hero image or heading — to fully load. Under 2.5 seconds is considered good. This is the metric most closely tied to “does the page feel fast.”
INP — how responsive the page feels
Interaction to Next Paint measures the delay between a visitor clicking or tapping something and the page actually responding. A page that loads fast but freezes for a second when you click a menu still fails here.
CLS — whether the layout jumps around
Cumulative Layout Shift measures how much content unexpectedly shifts position while loading — the classic case of trying to tap a button just as an ad or image loads above it and pushes it down. A low score means the page is visually stable as it loads.
Why it’s worth caring about
Google uses these as a ranking factor, but the bigger reason to care is simpler: they’re a reasonable proxy for whether visitors are actually having a good experience on your site. Fixing them tends to also fix the things visitors were quietly annoyed by.
Most Core Web Vitals problems trace back to image size, hosting resources, or plugin bloat — the same fixes covered in our website speed fixes guide.