What Are Core Web Vitals?
The three measures, what they mean in practice, and what usually causes each to fail.
What are Core Web Vitals?
Core Web Vitals are three measures of user experience: Largest Contentful Paint for loading, Interaction to Next Paint for responsiveness, and Cumulative Layout Shift for visual stability. The targets are 2.5 seconds, 200 milliseconds and 0.1. They are assessed on field data from real visitors rather than on a laboratory score.
These measures matter partly for search and mostly because they describe things visitors genuinely notice: waiting, unresponsiveness, and content moving under their finger.
What is Largest Contentful Paint?
The time until the largest visible element — usually a hero image, heading or banner — finishes rendering. It approximates when the page feels loaded. The target is under 2.5 seconds on mobile, and the most common causes of failure are oversized images and slow server response.
Identify the LCP element per template rather than per page. Fixing it once at template level usually improves hundreds of URLs.
What is Interaction to Next Paint?
How quickly the page visibly responds after a user interacts — tapping a button, opening a menu. The target is under 200 milliseconds. Failures are usually caused by heavy JavaScript occupying the main thread when the interaction occurs.
Third-party scripts such as chat widgets, analytics and advertising tags are frequent contributors, and deferring them often produces the largest improvement.
What is Cumulative Layout Shift?
How much visible content moves unexpectedly during loading, scored towards a target below 0.1. It is what causes someone to tap the wrong thing because the page shifted. Images without dimensions, late-loading fonts and injected banners are the usual causes.
Reserving space for anything that loads late — images, ads, embeds, cookie notices — eliminates most layout shift without any other change.
Why do my lab scores and field data disagree?
Lab tests use one device and one connection. Field data aggregates real visitors across varied hardware and networks, which for Indian traffic often means mid-range phones on mobile data. Field data is what is assessed, so that is what to optimise for.
Field data updates on a rolling window, so allow several weeks after a fix before judging whether it worked.
How much do Core Web Vitals affect rankings?
They are part of page experience signals and are generally a modest factor compared with content relevance and quality. The larger practical effect is on visitor behaviour — slow, unstable pages lose people before content quality matters at all.
Treat them as a conversion and usability priority that also helps search, rather than as an SEO tactic in isolation.
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