Core Web Vitals are the three metrics Google uses to describe the real-world experience of loading and using a page: Largest Contentful Paint for loading, Interaction to Next Paint for responsiveness, and Cumulative Layout Shift for visual stability. They are measured from real Chrome users and assessed at the 75th percentile of page loads. Google uses them as part of its page experience signals in ranking.
The three metrics and their thresholds
A page passes when at least 75% of visits meet the "good" threshold for all three metrics, measured separately for mobile and desktop.
- Largest Contentful Paint (LCP): good at 2.5 seconds or less, poor above 4 seconds
- Interaction to Next Paint (INP): good at 200 milliseconds or less, poor above 500 milliseconds
- Cumulative Layout Shift (CLS): good at 0.1 or less, poor above 0.25
Field data versus lab data
Field data comes from real users through the Chrome User Experience Report (CrUX). That is what Google uses for Search and what Search Console's Core Web Vitals report shows. It is a rolling 28-day window, so fixes take weeks to show. Pages or sites without enough traffic may have no field data at all.
Lab data comes from tools like Lighthouse that load a page once in a simulated environment. It is great for debugging, but it cannot measure INP directly (it has no real user interactions) and its numbers often differ from field data. A perfect Lighthouse score does not mean the page passes in the field.
How much they matter for rankings
Google has described page experience, including Core Web Vitals, as one of many signals and has said that great content can rank well even with poor page experience. In practice, Core Web Vitals are worth fixing because slow, janky pages lose visitors and conversions, and the ranking effect is a secondary benefit. Avoid promising traffic gains from passing them.
Typical issues on SaaS marketing sites
The usual culprits are predictable.
- Heavy hero videos, animations and large hero images delaying LCP
- Third-party scripts (chat widgets, analytics, A/B testing, consent banners) blocking the main thread and hurting INP
- Cookie banners, announcement bars and late-loading fonts shifting layout and hurting CLS
- Large JavaScript bundles from client-heavy frameworks delaying both rendering and interaction
Example
A homepage failing INP on mobile
Imagine a sales engagement SaaS, Cadencio, whose homepage passes LCP and CLS but fails INP on mobile. Profiling shows a chat widget, a session-recording script and a tag manager container all running large tasks right after load, so taps on the nav menu feel sluggish.
Delaying the chat widget until the visitor scrolls or is idle, and removing tags nobody uses, shortens the long tasks. The field data improves over the following 28-day window.
Common mistakes
Optimizing for Lighthouse instead of field data
Search uses real-user data. Check Search Console and CrUX, and use lab tools to find causes.
Testing only on fast desktop machines
Most failures show up on mid-range phones on mobile networks. Test with throttling or real devices.
Ignoring the templates that matter
Search Console groups URLs by similar pages. Fix shared templates (blog post, integration page) rather than individual URLs.
Questions
Yes. Interaction to Next Paint replaced First Input Delay as a Core Web Vital in March 2024.
CrUX only reports URLs and origins with enough real Chrome traffic. Low-traffic pages may be grouped with similar pages or have no data.
Google has not said they affect AI features specifically. Third-party AI search tools do not document using them. Treat them as a user-experience and Google Search concern.
