Interaction to Next Paint (INP)
Interaction to Next Paint (INP) is a Core Web Vital metric that measures the latency of all user interactions (clicks, taps, key presses) throughout the page lifecycle, reporting the worst interaction minus outliers.
INP replaced First Input Delay (FID) as a Core Web Vital in March 2024. While FID only measured the first interaction, INP measures all interactions throughout the page visit and reports the worst one, giving a much more accurate picture of real responsiveness.
Google considers INP good under 200ms, needs improvement between 200-500ms, and poor above 500ms. Poor INP is usually caused by long JavaScript tasks blocking the main thread during user interactions.
To optimize: break long tasks into smaller chunks using `setTimeout` or `scheduler.yield()`, defer non-critical JavaScript, minimize hydration cost in React/Next.js (use `React.lazy()` and `Suspense`), and avoid synchronous layout recalculations during event handlers.
Related terms
Core Web Vitals
Core Web Vitals are a set of three Google metrics — Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS) — that measure real-world user experience.
Largest Contentful Paint (LCP)
Largest Contentful Paint (LCP) is a Core Web Vital metric that measures the time from when the page starts loading to when the largest text block or image element is rendered in the viewport.
Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS) is a Core Web Vital metric that quantifies how much visible content unexpectedly shifts during the page lifecycle, measuring visual stability.
Page Speed
Page speed is the measurement of how quickly a web page's content loads and becomes interactive, typically measured by metrics like Time to First Byte (TTFB), First Contentful Paint (FCP), and Largest Contentful Paint (LCP).
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