Core Web Vitals Playbook for Indian Mobile Networks
Hit green vitals on 4G: image strategy, font loading, JS budgets, and measurement that matches field data.
1. Measure What Users Feel
Lab scores lie on fast office wifi. Anchor on CrUX field data for your actual Indian audience, then use lab runs to diagnose. Track LCP, INP, and CLS per template — homepage, category, and checkout behave differently and need separate budgets.
Set performance budgets in CI: fail builds that add more than 20KB of blocking JS or drop Lighthouse below 90. Budgets beat good intentions.
2. Images & Fonts First
Images are the usual LCP element: next/image with AVIF, explicit dimensions, and fetchpriority=high on the hero. Below-fold images lazy-load by default — verify, don't assume.
Fonts cause invisible-text flashes and layout shifts: display=swap, preload only the hero weight, and self-host subsets. One family, two weights maximum on marketing pages.
3. Tame JavaScript
INP suffers from main-thread congestion: split third-party scripts (chat, analytics, pixels) behind facades or web workers, defer everything non-critical past interaction, and virtualise long lists.
Audit quarterly — marketing pixels accumulate silently. Every script needs an owner and a measured conversion contribution, or it gets removed.
Frequently asked questions
What LCP should we target on 4G?
Under 2.5s for 75th percentile field data. Our builds typically land 1.2–1.8s on Moto-G-class devices.
Does INP matter more than FID now?
INP replaced FID as a Core Web Vital — it measures the whole interaction lifecycle, so event-handler bloat finally shows up in scores.