INP (Interaction to Next Paint)

INP observes the latency of all the interactions a user makes with a page, from the click, tap or key press until the browser paints the next frame showing a response, and reports a value that all or nearly all interactions were below. It replaced First Input Delay (FID) as a Core Web Vital because FID only measured the delay before the first interaction was handled.

web.dev rates INP of 200 milliseconds or less as good, 200 to 500 milliseconds as needing improvement, and above 500 milliseconds as poor, at the 75th percentile of page loads.

Poor INP is usually caused by JavaScript keeping the browser's main thread busy: large bundles, heavy third-party scripts such as tag managers, chat widgets and A/B testing tools, and event handlers that do too much work before updating the screen. Fixes include breaking up long tasks, removing or delaying non-essential scripts, and giving immediate visual feedback before doing slower work.