Core Web Vitals in the field

Your laptop is not your user

Lab tools run on a fast machine over a fast network and produce a repeatable best case. Field data comes from real devices and shows the distribution, which is where the interesting problems live.

Largest contentful paint is how long until the main content appears. Interaction to next paint measures the worst responsiveness the user actually experienced. Cumulative layout shift captures how much the page moved under them while they were reading it.

Look at the 75th percentile rather than the average. Performance work is about the bad sessions; the average hides them by definition.