Search and SEO
What is Core Web Vitals?
Core Web Vitals are three metrics Google uses to measure page experience: Largest Contentful Paint for loading, Interaction to Next Paint for responsiveness, and Cumulative Layout Shift for visual stability. They are assessed on real visitor data, not on laboratory tests.
Also called: CWV · LCP INP CLS
The three metrics and their targets
| Metric | Measures | Good |
|---|---|---|
| LCP | When the largest visible element finishes rendering | Under 2.5s |
| INP | How long the page takes to respond visibly to interaction | Under 200ms |
| CLS | How much content moves after being painted | Under 0.1 |
Field data versus lab data
Assessment uses field data — what real visitors experienced, on their own devices and connections, aggregated over a rolling 28-day window. A lab tool such as Lighthouse simulates one load on one simulated device and is a diagnostic rather than a score.
When the two disagree, believe the field data. It is what is used, and it is what your customers actually felt.
How much they affect rankings
Less than most vendors imply and more than zero — realistically a tie-breaker between pages that are otherwise comparable. The better business case is conversion: slow pages lose customers regardless of what any search engine thinks.
Where this is covered in depth
A definition can only go so far. Core Web Vitals, and the order that actually reduces them covers this properly — 3 minutes, free, no email required.
Who wrote this
Anas Bin Masud builds e-commerce sites and does technical SEO for businesses in the UK, Canada and Pakistan. These definitions come from client work rather than from a content brief — where an entry describes a mistake, it is usually one found on a real site. More about how I work.