Interaction to Next Paint (INP) measures how fast a web page visibly responds when you interact with it. Click a button, tap a menu, type in a field: INP records the time between that action and the next moment the screen actually updates. A low number means the page feels instant; a high one means it feels laggy.
Imagine pressing a light switch and waiting half a second before the bulb comes on. The light works, but that pause feels broken. INP catches exactly that gap on a website, across every interaction during a visit, and reports the worst ones so you see what real users feel. It is one of the three Core Web Vitals and replaced the older First Input Delay in 2024 because FID only checked the first click.
The usual culprit behind a bad INP is too much JavaScript running on the main thread at once. A browser can only do one thing at a time on that thread, so when a JavaScript library hogs it, clicks pile up in a queue and the screen stalls until the queue clears. Splitting code into smaller chunks, doing less work per interaction, and deferring non-urgent scripts all help. Google reports INP from real visits through the Chrome User Experience Report, so it reflects actual phones and laptops, not a fast test machine. A page can feel fine on a developer’s MacBook and score badly for someone on a mid-range Android. Because it is part of the Largest Contentful Paint family of page-experience signals, a poor INP can quietly hold back rankings even when the rest of the site looks healthy.
At TopDevs we treat INP as a real product quality signal, not a vanity score, and we tune interactions until a page reacts the instant someone touches it.
