INP (Interaction to Next Paint)
Measures the responsiveness of a page to user interactions. Target: under 200ms.
Interaction to Next Paint (INP) measures how quickly a page responds visibly after a user interacts — a tap, a click, a keypress. It replaced First Input Delay as a Core Web Vital in 2024, and a good score is 200 milliseconds or less. Long JavaScript tasks blocking the main thread are the usual cause of a poor one.
Definition
INP measures the latency of all user interactions (clicks, taps, keyboard input) throughout a page's lifecycle. It replaced FID (First Input Delay) in March 2024 as a Core Web Vital because it measures ALL interactions, not just the first one.
Target: under 200ms. INP is the worst interaction latency observed, ignoring the single worst outlier.
Why It Matters
A page that looks fast but freezes when you click a button is a terrible experience. INP captures this. Heavy JavaScript execution, long tasks, and unoptimized event handlers are the main culprits.
Example
A dropdown menu that takes 450ms to open after clicking has poor INP. Fix: break long JavaScript tasks into smaller chunks using requestIdleCallback or scheduler.yield().
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