What is Interaction to Next Paint?
Interaction to Next Paint (INP) measures a page's overall responsiveness to user interactions like clicks and taps. A good INP is 200 milliseconds or faster.
Why Interaction to Next Paint matters
Interaction to Next Paint measures how long the page takes to visibly respond after a tap, click or key press, across the whole visit, and reports close to the worst case. It replaced First Input Delay as a Core Web Vital in March 2024 because FID only measured the first interaction and only the delay before the handler ran. INP includes the handler itself and the time to paint the result; 200 ms or less is good.
Slow INP almost always means the main thread is busy: long JavaScript tasks from frameworks, analytics and tag managers, expensive event handlers, or layout thrashing when a handler reads and writes the DOM in a loop. Breaking long tasks up, deferring non-essential scripts, and giving the browser a chance to paint before doing heavy work are the standard fixes.
Example
Yielding to the browser so the click paints before the heavy work:
button.addEventListener('click', async () => {
button.textContent = 'Saving…'; // paints immediately
await new Promise(r => setTimeout(r)); // yield to the main thread
runExpensiveUpdate();
});The visible response happens first; the expensive part runs after the paint.
Common mistakes
- •Third-party scripts (chat widgets, tag managers) hogging the main thread on every page.
- •Handlers that synchronously rebuild large parts of the page.
- •Optimising the lab TBT number and assuming field INP will follow; it often does not.
How Webmatik checks it
Webmatik's Real visitor click response check reports field INP from the Chrome UX Report, and the Button & click response time and Page responsiveness while loading checks report the Lighthouse figures that usually explain it.
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