What is Interaction to Next Paint?
INP: the Core Web Vital that measures responsiveness. It captures the latency of every click, tap, and keyboard interaction throughout a page's lifecycle, then reports a value near the worst-case. A good INP is 200 milliseconds or less, meaning the page visually responds to user input almost instantly.
My perspective
In practice
INP replaced First Input Delay (FID) in March 2024 because FID only measured the first interaction. Poor INP usually traces back to long JavaScript tasks blocking the main thread: heavy frameworks, unoptimized event handlers, or layout thrashing. Solutions include code splitting, deferring non-critical scripts, and breaking long tasks into smaller chunks with requestIdleCallback or scheduler.yield().