Core Web Vitals
A set of specific factors that Google considers important in a webpage's overall user experience.
Detailed Explanation
Core Web Vitals consist of three specific page speed and user interaction measurements: Largest Contentful Paint (loading performance), First Input Delay (interactivity), and Cumulative Layout Shift (visual stability). Since 2021, these metrics have been official ranking signals. A 'passing' score across all three is essential for maximizing search visibility and user retention.
Quick Summary
Core Web Vitals are Google's three real-user metrics for page experience: LCP (loading), INP (interactivity), and CLS (visual stability). They influence search ranking and correlate strongly with conversion and engagement.
Key Takeaways
- LCP (Largest Contentful Paint): time until the largest above-the-fold element renders. Target: <2.5s.
- INP (Interaction to Next Paint): worst-case interaction latency over the page lifecycle. Target: <200ms. Replaced FID in 2024.
- CLS (Cumulative Layout Shift): unexpected layout movement. Target: <0.1.
- Measured in the field via Chrome User Experience Report (CrUX), not just synthetic tools, real users on real devices.
- Pass = 75th percentile across all three on both mobile and desktop.
When to use it
- SEO optimization, passing CWV is part of Google's page experience ranking signal.
- Performance budgets in CI to catch regressions before they reach users.
- Mobile commerce, where slow LCP and high INP cost conversions directly.
- Diagnosing UX complaints by mapping them to specific Vitals.
Common Mistakes
- Optimizing only with Lighthouse (synthetic, lab) and ignoring CrUX (real-user, field), they often disagree.
- Treating CWV as a 100/100 score chase rather than the 75th-percentile threshold it actually measures.
- Improving LCP for the homepage only; CWV is per-page-type and ranking impact follows.
- Ignoring INP after FID was retired; INP is stricter and catches issues FID missed.
Core Web Vitals, Frequently Asked
How do I measure real-user CWV?
Use the web-vitals JS library to send metrics to your analytics, plus Google Search Console (CrUX-based) for the official numbers Google uses. Synthetic tools like PageSpeed Insights and Lighthouse are useful for debugging but not for the official scorecard.
Is CWV really a ranking factor?
Yes, but a tie-breaker, not a primary signal. Content relevance, links, and authority dominate. Improving CWV won't outrank a better page, but failing CWV can lose ranking against equally-good pages.