Core Web Vitals are Google's defined quality metrics for web page user experience. They measure loading speed (LCP), responsiveness (INP), and visual stability (CLS) in numbers. They are the core of the page experience signals factored into search rankings, and a baseline element of technical SEO that reduces bounce.
Three Core Metrics
| Metric | What It Measures | Good Threshold |
|---|---|---|
| LCP (Largest Contentful Paint) | Loading speed of main content | Within 2.5s |
| INP (Interaction to Next Paint) | Responsiveness to user input | Within 200ms |
| CLS (Cumulative Layout Shift) | Degree of visual element shifting | 0.1 or below |
INP became an official metric in March 2024, replacing the previous FID (First Input Delay). It does not measure just the first input delay - it evaluates the responsiveness of every interaction across the entire page session.
Impact on Rankings and Conversions
Core Web Vitals affect rankings as part of the Page Experience signals. The impact itself is smaller than content quality, but it makes a decisive difference for keywords with similar competition.
What matters more is user behavior.
- Slow pages raise the bounce rate
- Shifting layouts increase misclicks and break trust
- Slow responsiveness directly lowers the conversion rate
Many analyses show that a 1-second increase in LCP noticeably raises bounce. Treat Core Web Vitals as a revenue metric, not an SEO score.
Improvement Points by Metric
- LCP: Optimize images, shorten server response, prioritize loading of key resources
- INP: Split heavy JavaScript, reduce main thread work
- CLS: Specify explicit dimensions for image and ad areas, stabilize font loading
Manage desktop and mobile scores separately. Mobile is usually lower, so prioritize it.
How to Check
- Search Console "Core Web Vitals" report: real-user data (field data)
- PageSpeed Insights: provides field data and diagnostics together
- Lighthouse: development environment simulation (lab data)
The standard flow is to find causes with lab data and confirm actual improvement with field data.
Notes
Core Web Vitals are not a box to check once met - they are the baseline premise for not undercutting content value. 238lab diagnoses technical metrics and content signals together from an SEO and GEO perspective, lifting both rankings and conversions at once.