What is INP (Interaction to Next Paint)?
A Core Web Vital measuring the time from a user input (click, tap, keypress) to the next visual update. Target: under 200ms for a 'good' score. Replaced FID in March 2024.
Interaction to Next Paint (INP) measures how responsive your page feels — specifically, how long after a user clicks, taps, or types until the visible content updates. It replaced First Input Delay (FID) as a Core Web Vital in March 2024 because FID only measured the very first interaction; INP measures every interaction during the page's lifetime and reports the worst (75th percentile). Google's thresholds: Good ≤ 200ms, Needs Improvement 200-500ms, Poor > 500ms. INP killers: long JavaScript tasks blocking the main thread (especially heavy React renders), synchronous storage access in event handlers, layout-thrashing animations. Fixes: break long tasks with requestIdleCallback or scheduler.yield(), defer non-critical effects, use CSS transforms instead of layout-affecting properties, lazy-load below-the-fold components.