Core Web Vitals are Google’s three metrics for the part of page performance users actually feel:
- LCP (Largest Contentful Paint), how quickly the biggest visible element renders. Good: under 2.5s.
- INP (Interaction to Next Paint), how quickly the page responds to taps and clicks. Good: under 200ms.
- CLS (Cumulative Layout Shift), how much things jump around as the page loads. Good: under 0.1.
Why it matters
Core Web Vitals are a Google ranking signal and the strongest correlate of conversion rate in real-user studies. A page that hits all three feels professional; a page that misses any feels like the kind of site you’d back-button out of.
Common mistakes
- Optimizing for lab metrics only. Lighthouse scores don’t equal real-user experience. Use the Chrome User Experience Report (CrUX) or your own RUM data.
- Ignoring CLS from late-loading images. Always set explicit
widthandheighton<img>tags so the browser can reserve space. - Loading too much JavaScript on the homepage. First Load JS over 100 KB on a marketing page is a problem worth fixing.