What are Core Web Vitals in plain English?

Largest Contentful Paint is how long until the biggest thing on screen — usually the headline or the hero image — has actually appeared. It is the closest machine equivalent to the moment a visitor stops looking at a blank rectangle.

Interaction to Next Paint is how long the page takes to visibly respond after someone taps or clicks. Not how long the whole action takes; how long before anything happens at all. A page that looks finished but ignores a tap for half a second fails here while looking fine.

Cumulative Layout Shift is how much the content jumps around while loading. It is the metric behind tapping a link and hitting a different one because an image finished loading and pushed the page down.

A lab test loads your page once, on a simulated device, under controlled conditions. A field measurement is collected from real Chrome users on real phones on real connections over the previous 28 days. Both are useful; only the second one is what Google reports as your Core Web Vitals.

This is why a site can show a perfect test score and still fail. The test was run somewhere kinder than where the visitors are. It is also why a site with little traffic shows no field data at all — there are not enough visitors to build a sample, and the lab number is the best available estimate rather than the real answer.

The thresholds are graded at the 75th percentile. A passing LCP means three quarters of the measured visits showed the main content within 2.5 seconds. It says nothing about the remaining quarter, who may have waited considerably longer.

So good is a floor, not a target. It marks where the metric stops counting against you, not where visitors stop leaving. Building to the threshold leaves no margin for the bad days — the weak signal, the older phone, the afternoon an image host is slow — and those are the days the margin was for.

Our pre-deploy gate measures every route on this site and refuses the deploy if any of them regress. On 16 September 2026, across all twelve routes: Largest Contentful Paint 420 to 663 milliseconds on desktop and 1,503 to 2,026 milliseconds on mobile, with Cumulative Layout Shift at zero on every route.

The caveat is the point of section 02. Those are lab numbers, produced by Lighthouse against a simulated mid-range phone on a throttled connection. They are not field data, because this site does not yet have the traffic volume Google needs to collect a field sample. We publish them because a measured lab number with its conditions stated is worth more than a claim, not because it is the same thing as real visitors.