Frontend Full-Chain Performance Optimization Guide A frontend performance diagnostic and optimization system based on Web Vitals core metrics. Core principle: User-centric — optimization is about doing less, not more. Metric Threshold Quick Reference | Metric | Good | Needs Improvement | Poor | Unit | Focus | | ------ | ------ | ------------------- | ------ | ------ | -------- | | LCP | ≤ 2.5s | 2.5s - 4s | 4s | Time | Largest Contentful Paint | | FCP | ≤ 1.8s | 1.8s - 3s | 3s | Time | First Contentful Paint | | INP | ≤ 200ms | 200ms - 500ms | 500ms | Time | Interaction to Next Paint | | CLS…