Core Web Vitals Checklist for Product Launches (2026)

LCP: fix the hero, not the footer

Largest Contentful Paint fails when the hero image, font, or server TTFB is slow — not because of third-party scripts at the bottom of the page.

Prioritize hero media with fetchpriority="high", preload critical fonts, and fix server TTFB before blaming React. Never lazy-load the LCP element. MedLynx cut LCP 41% by fixing the appointment banner and font chain — not by deferring analytics.

INP: main thread discipline

Interaction to Next Paint replaced FID in 2024. Break long tasks over 50ms, defer non-critical JS, and audit event handlers on interactive pages — checkout, filters, onboarding steps.

At Shriram we assign INP budgets per template in discovery. Rahul runs Lighthouse CI on PRs; merges blocked on regression for money pages.

CLS: reserve space or pay twice

Cumulative Layout Shift comes from images, embeds, and banners injected above content after load. Reserve aspect-ratio boxes, never inject cookie banners over the hero, and test with slow 3G — not just fiber on a MacBook.

Assign ownership before kickoff

CWV is not "the frontend person's problem." Vikas owns budgets at Shriram; product, design, and backend share the score. Template-level targets in writing prevent the "we'll optimize later" trap.

Measure in CI and field data

Lab scores in Lighthouse CI catch regressions on PRs. Field data in CrUX and GSC shows what real users experience. Both matter — lab for prevention, field for truth.

Pre-launch checklist

1. LCP element identified and not lazy-loaded
2. Fonts preloaded; subset for non-Latin scripts tested
3. INP under 200ms on interactive templates
4. CLS under 0.1 with cookie/consent banner positioned safely
5. Regression tests in CI for money pages