Core Web Vitals: A Senior Engineer's Guide

Core Web Vitals: A Senior Engineer's Guide A comprehensive guide to measuring and optimizing Core Web Vitals for system design interviews. 1. What Are Core Web Vitals? Core Web Vitals are Google's standardized metrics for measuring user experience. They directly impact SEO rankings . ┌─────────────────────────────────────────────────────────────┐ │ CORE WEB VITALS │ ├──────────────────┬──────────────────┬──────────────────────┤ │ LCP │ INP │ CLS │ │ Loading │ Interactivity │ Visual Stability │ │ │ │ │ │ < 2.5s GOOD │ < 200ms GOOD │ < 0.1 GOOD │ │ 2.5-4s NEEDS │ 200-500ms NEEDS │ 0.1-0.25 NEEDS │ │ > 4s POOR │ > 500ms POOR │ > 0.25 POOR │ └──────────────────┴──────────────────┴──────────────────────┘ 2. LCP (Largest Contentful Paint) What It Measures The time it takes for the largest visible element to render in the viewport. ┌─────────────────────────────────────────────────────────────┐ │ Timeline │ │ │ │ 0ms ─────────────────────────────────────────────▶ 2500ms │ │ │ │ │ │ │ │ │ └──