Technical SEO
Core Web Vitals
Core Web Vitals are Google's three page-experience metrics: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness), and Cumulative Layout Shift (visual stability).
They are a ranking signal, and INP replaced First Input Delay in March 2024. A page that loads fast but jumps around as it renders will still fail CLS and lose ground. Good scores improve both rankings and conversions.
Lab scores and field data disagree more often than teams expect, and only one of them affects search. Lighthouse runs a simulated load on a throttled connection, which is useful for debugging but is not what Google uses. The Search Console report shows the Chrome User Experience Report, which is real visits at the 75th percentile over 28 days. That lag matters: after a fix ships, field data takes weeks to reflect it, so judging the change by next-day lab scores gives a misleading answer in both directions.
Example
A landing page scores 96 in Lighthouse on a developer's laptop, yet Search Console shows it failing: real-user LCP is 4.1 seconds at the 75th percentile. The users are on mid-range phones over 4G, which the lab test never simulated. Compressing the hero image and inlining critical CSS brings field LCP to 2.2s six weeks later.
Frequently asked questions
- How much do Core Web Vitals affect rankings?
- Less than most people assume. They are a page-experience signal that can act as a tiebreaker between similar pages, but relevance and authority matter far more. Improve them for user experience and conversion rate first; treat any ranking benefit as a bonus.
- What are good Core Web Vitals scores?
- Largest Contentful Paint under 2.5 seconds, Interaction to Next Paint under 200 milliseconds, and Cumulative Layout Shift under 0.1, measured at the 75th percentile of real users. Lab tools like Lighthouse estimate these, but field data in Search Console is what Google actually uses.
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