Core Web Vitals
Google's three tests of a good page visit, in plain language.
By the Vulo Labs team · Last updated
What are Core Web Vitals and what scores are good?
Core Web Vitals are Google's three measures of real-world page experience. Largest Contentful Paint (LCP) measures loading and is good at 2.5 seconds or less. Interaction to Next Paint (INP) measures responsiveness and is good at 200 milliseconds or less. Cumulative Layout Shift (CLS) measures visual stability and is good at 0.1 or less.
The three vitals
Loading, measured by Largest Contentful Paint (LCP): how quickly the main content appears, good at 2.5 seconds or less. Responsiveness, measured by Interaction to Next Paint (INP): how quickly the page reacts when someone taps or clicks, good at 200 milliseconds or less. Visual stability, measured by Cumulative Layout Shift (CLS): whether things jump around while loading, good at 0.1 or less.
Common causes
Slow loading is often a large hero image or slow server. Poor responsiveness usually comes from heavy scripts. Layout shifts come from images without set dimensions and late-loading fonts or ads.
How to improve
Compress and size images, delay scripts you do not need immediately, reserve space for media, and use caching.
Key takeaways
- Fix the biggest image first
- Reduce heavy scripts
- Set image dimensions
- Re-test after changes
Core Web Vitals: frequently asked questions
Yes. Interaction to Next Paint replaced First Input Delay as a Core Web Vital in March 2024. INP measures responsiveness across the whole visit, not just the first interaction.
They are part of Google's page experience signals. Google says good page experience helps, but relevant, helpful content matters more.
Field data comes from real Chrome users (the Chrome UX Report) at the 75th percentile of visits. Lab tools such as Lighthouse estimate them for debugging.
Sources and further reading
A speedometer for your website, plus what to fix first.