INP (Interaction to Next Paint)

INP measures the delay between a tap, click, or keypress and the next visual update, sampled across the whole visit rather than just the first interaction like the old FID metric. The usual cause of a bad score is heavy JavaScript blocking the main thread — large third-party scripts, unbroken long tasks, or expensive event handlers. Break work into smaller chunks, defer non-critical scripts, and use techniques like requestIdleCallback so the browser can paint between tasks.