"Core Web Vitals" gets thrown around a lot in SEO conversations, usually followed by a vague instruction to "make your site faster." That's true, but it's not the whole picture — Google is actually measuring three specific, named things, and each one responds to different fixes. Here's what they mean without the jargon.
Largest Contentful Paint (LCP): how long until the page feels loaded
LCP measures how long it takes for the biggest visible element on the screen — usually a hero image, a heading, or a background video — to fully render. It's meant to approximate the moment a visitor feels like the page has actually loaded, rather than just started to.
The most common causes of a slow LCP are large, uncompressed images and hero videos, render-blocking CSS or JavaScript loading before the visible content, and slow server response times. The fix is usually some combination of: compressing and properly sizing images, deferring anything that isn't needed for the first screen, and using a poster image so the page has something visible before a background video finishes loading.
Cumulative Layout Shift (CLS): does the page jump around while it loads
You've felt this even if you didn't know the name for it — you go to tap a button, and right as your finger lands, an image finishes loading above it and shoves the whole page down, so you tap the wrong thing. CLS measures how much visible content unexpectedly shifts around during load.
The fix is almost always to reserve space in advance: give images and video elements explicit width and height (or an aspect-ratio in CSS) so the browser can block out their space before they've finished loading. Ads, embeds, and web fonts that swap in late are other common culprits.
Interaction to Next Paint (INP): how responsive the page feels when you actually use it
INP measures how long it takes for the page to visibly respond after you click a button, open a menu, or submit a form — across the whole session, not just the first click. Heavy, unoptimized JavaScript is the usual cause. Trimming unused scripts, loading non-essential JavaScript later rather than all upfront, and breaking up large scripts into smaller chunks all help.
None of these three metrics are abstract "SEO tricks" — they're Google's attempt to measure the same thing a frustrated visitor already feels: does this page load, does it hold still, and does it respond when I touch it.
So how much does this actually affect rankings?
Core Web Vitals are one of many ranking factors, and generally a smaller one than the strength of your content and your overall relevance to the search. But they matter in two real ways: as a tiebreaker between otherwise similar pages, and — probably more importantly — as a direct driver of whether visitors stick around once they land. A slow, jumpy page loses visitors before it ever gets the chance to convert them, no matter where it ranks.
Where to check your own numbers
Google's free PageSpeed Insights tool will score your actual live pages against all three metrics and point out specific offending elements — it's the same underlying data Google uses for ranking, so it's worth checking periodically rather than guessing.