INP (Interaction to Next Paint)

Definition

Interaction to Next Paint (INP) replaced First Input Delay (FID) as a Core Web Vital in March 2024. While FID only measured the delay of the first interaction, INP measures the latency of all interactions throughout the page's lifecycle and reports the worst one (with outliers excluded). A good INP score is 200 milliseconds or less. Poor INP is usually caused by heavy JavaScript execution, long tasks blocking the main thread, or excessive DOM size. Optimize INP by breaking up long tasks, using web workers for heavy computation, reducing DOM size, and deferring non-critical JavaScript.