Core Web Vitals are the three metrics Google uses to measure the technical experience of a page. They have been an official ranking factor since 2021 and in 2026 they still matter, especially on mobile — and a fast page is also processed better by AI systems.
The three metrics and their thresholds
- LCP (Largest Contentful Paint) — loading speed of the main content. Good: under 2.5 s.
- INP (Interaction to Next Paint) — responsiveness to interactions. It replaced FID. Good: under 200 ms; 200 to 500 ms needs improvement; over 500 ms is poor.
- CLS (Cumulative Layout Shift) — visual stability of the layout. Good: under 0.1.
How to optimize LCP
- Compress and serve images in modern formats (WebP/AVIF), at the right dimensions.
- Preload the main resource (hero image or font) and use a CDN.
- Reduce server response time and render-blocking CSS.
How to optimize INP
- Reduce and split heavy JavaScript: less work on the main thread.
- Move expensive computations into web workers.
- Optimize event handlers and avoid synchronous layouts during interaction.
How to optimize CLS
- Always set width and height (or aspect-ratio) on images and videos.
- Reserve space for banners, ads and embeds.
- Load fonts with
font-display: swapand preload them to avoid jumps.
How to measure them
Use field data (CrUX/Search Console) alongside lab tests: real users count more than a single test. Start from mobile, where problems show up most.
Put them into practice
Core Web Vitals are only one part of the technical experience: HTTPS, mobile, canonical and structure matter too. The free audit of your site checks these signals and returns the priorities to act on first. For the on-page side, you can start from the meta tag checker of a page.