Core Web Vitals are Google's attempt to measure how a page feels to a real person. They influence search rankings, but more importantly they correlate with revenue — slow, jumpy pages lose customers. There are three to know.
Largest Contentful Paint (LCP)
LCP measures how quickly the biggest thing on screen — usually a hero image or headline — appears. Aim for under 2.5 seconds. The usual culprits are heavy images, slow servers and render-blocking code. Compressing images, serving modern formats like WebP and trimming unused scripts almost always helps.
Interaction to Next Paint (INP)
INP measures responsiveness: when someone taps or clicks, how long before the page reacts? Sluggishness here usually comes from too much JavaScript running at once. Splitting code, deferring what isn't needed immediately and keeping the main thread free all improve it.
Cumulative Layout Shift (CLS)
CLS measures visual stability — the annoyance of a button jumping just as you go to tap it. The fix is mostly discipline: set explicit width and height on images and embeds, reserve space for anything that loads late, and avoid injecting content above what's already on screen.
Where to start
Measure first. Tools like PageSpeed Insights and the Chrome User Experience Report show real-world numbers, not guesses. Fix the biggest offender, measure again, repeat. Performance work compounds: each improvement makes the next easier to see.
None of this needs to be mysterious. Treat speed as a feature with an owner and a target, and it stops being an afterthought.