INP now matters as much as LCP. Concrete techniques to cut interaction latency in the field — and the measurement traps.
What INP measures
INP (Interaction to Next Paint) measures the delay from a user’s click/tap to the moment the screen actually changes. Where LCP asks "how fast did it load?", INP asks "how responsive does it feel?". It has been a ranking signal since 2024 and is the weakest link on most sites.
Break up long tasks
What kills INP is usually long JavaScript tasks that block the main thread. Splitting big work with yields, deferring non-critical work until after the interaction, and cutting needless re-renders often drops INP below 200ms on its own.
Measure with field data
Lighthouse is lab data; INP is measured on real users (CrUX / RUM). Looking only at the lab score misleads you. We add a lightweight RUM to every project and segment INP by device and page type, because an average hides the jank a mobile user actually feels.
