Editorial guide based on official documentation; not a hands-on product test.
Understand what LCP, INP, and CLS measure, where to find real-user data, and how to choose the first performance fix.
What the three numbers describe
Largest Contentful Paint (LCP) looks at when the main visible content appears. Interaction to Next Paint (INP) describes how quickly the page responds to a user interaction. Cumulative Layout Shift (CLS) captures unexpected movement of visible content. They represent different experiences, so a site can pass one and fail another. Google’s published “good” thresholds are LCP at or below 2.5 seconds, INP at or below 200 milliseconds, and CLS at or below 0.1, assessed at the 75th percentile of page loads.
Use field data for the user story
PageSpeed Insights may show real-user field data and a separate lab test. Field data combines actual visits and can reflect device, network, and interaction differences. Lab data helps reproduce a single scenario and locate causes. Do not compare a field percentile directly with one Lighthouse run as if they were the same sample. For a low-traffic URL, use available origin-level data cautiously and instrument your own representative pages if possible.
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