Interaction to Next Paint

Interaction to Next Paint measures the longest time between a user input — a click, tap, or keypress — and the next time the browser paints a visible response. Where the older First Input Delay only measured the first interaction, INP samples every interaction during the visit and reports the worst.

The target is under 200ms; anything above 500ms is considered poor. INP exposes the JavaScript work that runs in response to interactions: an expensive `setState`, a large rerender, a synchronous network request that blocks the click handler. Fixing INP is harder than fixing TBT because it’s about runtime behavior, not load behavior.

The usual wins: defer non-critical work to `requestIdleCallback`, batch state updates, avoid synchronous layouts inside event handlers, and use `useTransition` (or its equivalent) to keep urgent updates fast.