metrics
INP (Interaction to Next Paint)
How responsive a page feels after the user clicks/taps — replaces FID as the Core Web Vitals interactivity metric.
Definition
Interaction to Next Paint is the worst-case time between a user input (click, tap, keypress) and the next paint with visible feedback. Replaced First Input Delay (FID) in March 2024. Good < 200ms; needs improvement 200–500ms; poor > 500ms. Captures sluggishness humans actually feel, unlike FID which only measured first input.
Example
User clicks 'add to cart'. If the button visual state updates in 150ms = good. If a long JS task blocks for 800ms = poor INP.How to optimize
Break long JS tasks into smaller chunks. Defer non-critical work to requestIdleCallback. Use web workers for heavy computation. Measure with Chrome DevTools.