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Term

INP (Interaction to Next Paint)

INP measures how quickly a page responds to user interactions. A Core Web Vital since March 2024 (replacing FID) — "good" threshold is ≤ 200 ms.

INP — explained in more detail

INP (Interaction to Next Paint) measures the latency between a user interaction (click, tap, keypress) and the next visual update of the page. Unlike its predecessor FID, INP captures all interactions during a session and reports the worst one (or the 98th percentile when there are many) — not just the first.

Thresholds: ≤ 200 ms = good, ≤ 500 ms = needs improvement, > 500 ms = poor. INP has been an official Core Web Vital since March 2024 and replaces FID. The score that counts is the 75th percentile from CrUX field data.

Example / In practice

INP killers are usually long-running JavaScript tasks: heavy hydration, unbatched third-party tracking, large event handlers, synchronous layout. Levers: break up long tasks (scheduler.yield(), requestIdleCallback), defer hydration, lazy-load third-party scripts, move CPU-heavy work into Web Workers.

Distinction from similar terms

FID (First Input Delay) only measured the first interaction and only the delay until the handler started — not the full rendering. INP is significantly stricter and more realistic because it captures the entire interaction experience.

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