Core Web Vitals are three metrics Google uses to describe page experience, all measured from real visitors rather than from a test. They are the closest thing to an objective answer to whether a page feels fast, and they tend to be worst exactly where it matters most: on a phone, on a weak connection, on the page somebody landed on in a hurry.
Briefly explained
- Three metrics: LCP, INP and CLS.
- The figures come from people who actually visited, not from a simulation.
- A tiebreaker for ranking, and a real factor in conversion.
- Usually broken by images, scripts and hosting.
What do the three measure?
- Largest Contentful Paint (LCP): How long until the main content is visible. The headline number.
- Interaction to Next Paint (INP): The delay between a tap and the page doing something about it.
- Cumulative Layout Shift (CLS): Whether things move under the reader’s thumb as the page assembles. The reason people tap the wrong button.
Why does lab data disagree with the report?
Because they measure different things.
A speed test runs once, on a simulated device, in good conditions. Search Console reports what actually happened to real visitors over the past 28 days, on whatever phones and connections they had.
A perfect lab score sitting next to failing field data is normal. Trust the field data, and expect weeks rather than days before a fix shows up in it.
Why does it matter beyond ranking?
The damage is done before ranking becomes relevant at all.
Most urgent searches happen on a phone, often on a poor connection. A page that takes several seconds to show a phone number loses the caller outright. And in paid search, page experience feeds Quality Score, so a slow page raises what you pay for the click as well as wasting it.
What usually causes failures?
- Uncompressed hero images and background video
- Chat widgets, tracking tags and review badges loading before the content
- Fonts that swap in late and shift everything down the page
- Shared hosting with a slow server response
The fix is rarely one setting. It is image discipline, restraint with third-party scripts, and hosting that answers quickly.
What do the terms mean?
- Field data: Measurements from real visitors. What Google uses.
- Lab data: A simulated test. Useful for debugging, not for judging.
- LCP: Time until the main content appears.
- INP: Responsiveness to taps and clicks.
- CLS: How much the layout moves while loading.
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