Frontend Performance Playbook 2025

Practical tactics that move the needle on real devices.

Images

• Use modern formats (AVIF/WebP)
• Explicit width/height to avoid CLS
• Lazy-load below the fold

JavaScript

• Remove unused packages, split by route
• Ship less JS to the client; prefer RSC

Network

• HTTP/3 + preconnect critical origins
• Cache aggressively at the edge

Monitoring

• Field data > lab data; use RUM and synthetic together

Small wins stack up. Measure, then optimize.