FID / INP is configured to meet the 100ms / 200ms threshold

Interaction to Next Paint (INP) measures how quickly a page responds to any user gesture — click, tap, or keyboard input. Google replaced FID with INP as a Core Web Vitals metric in March 2024 because INP captures the full session, not just the first interaction. INP above 200ms is classified as 'poor' and is driven almost entirely by long JavaScript tasks blocking the main thread. Marketing pages are high-risk: analytics, chat, heatmap, and ad pixel scripts are routinely copy-pasted from vendor docs as synchronous <script> tags in <head>, each forcing the browser to stop parsing HTML until the script downloads and executes. On mid-range Android, three synchronous third-party scripts can easily add 300–500ms of blocking time, breaching the INP threshold and degrading the Core Web Vitals page experience score.

Defer all non-critical JavaScript using the Next.js Script component — it enforces the right loading strategy and prevents accidental synchronous loading.

import Script from 'next/script'

// Analytics — wait until page is interactive
<Script
  src="https://www.googletagmanager.com/gtag/js?id=G-XXXXXX"
  strategy="afterInteractive"
/>

// Chat widget — defer until browser is idle
<Script
  src="https://cdn.intercom.com/widget.js"
  strategy="lazyOnload"
/>

For INP ≤ 200ms on mid-range mobile, keep total JavaScript on the critical rendering path under 150KB compressed. Run npx @next/bundle-analyzer to identify oversized chunks contributing to parse time.