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Interaction to Next Paint (INP) — Slow Response to User Interactions Fix

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Overview

Fix high Interaction to Next Paint (INP) scores where button clicks, taps, and keyboard inputs feel sluggish due to long JavaScript tasks blocking the main thread.

Key Details

  • INP replaced FID (First Input Delay) as a Core Web Vital in March 2024
  • INP measures responsiveness: the time from user interaction to the next visual update
  • Google considers INP good if under 200ms, needs improvement between 200-500ms, and poor over 500ms
  • Unlike FID which only measured the first interaction, INP considers ALL interactions during the page lifecycle
  • Long JavaScript tasks (>50ms) block the main thread and delay response to user input

Common Causes

  • Heavy JavaScript execution blocking the main thread during user interactions
  • Third-party scripts (analytics, ads, chat widgets) consuming main thread time
  • Large DOM size causing slow rendering updates after interactions
  • Synchronous layout calculations (forced reflows) triggered by JavaScript

Steps

  1. 1Measure INP: Chrome DevTools > Performance tab > record interactions > check 'Interactions' track
  2. 2Break up long tasks: split heavy JS work into smaller chunks using requestIdleCallback or setTimeout
  3. 3Defer third-party scripts: load analytics and non-critical scripts with async or defer attributes
  4. 4Use Web Workers for heavy computations to keep the main thread free for user interactions
  5. 5Reduce DOM size: large DOMs (>1000 elements) cause slow style and layout recalculations

Tags

inpcore-web-vitalsinteractionresponsivenessmain-thread

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browser-largest-contentful-paint-slowbrowser-cumulative-layout-shift-issues

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Frequently Asked Questions

FID only measured the delay of the first interaction. INP measures all interactions throughout the page lifecycle and reports the worst (or near-worst) interaction latency. INP gives a more complete picture of page responsiveness.