Core Web Vitals Code Fix Reference

The Core Web Vitals cheatsheet explains what to fix. This guide shows you how — with actual code. It's a developer-focused reference for the most common CWV issues, with implementation examples for the frameworks and setups where those issues appear most often.

LCP fixes covered: responsive image markup with width/height attributes, next-gen format implementation in HTML and WordPress, preload hint syntax for hero images, and server-side rendering considerations. There are also nginx and Apache cache-header configurations that improve TTFB, which affects LCP indirectly.

CLS fixes covered: aspect-ratio CSS for images and iframes, reserved space for ad slots, font-display swap implementation, and controlling layout shifts from dynamically injected elements. Each pattern includes a before/after code comparison.

INP fixes covered: patterns for deferring non-critical JavaScript, splitting long tasks with scheduler.postTask or setTimeout, passive event listener configuration, and input debouncing. There's also a section on third-party script management — isolating analytics, chat widgets, and marketing tags that create long tasks.

The guide is framework-agnostic but includes notes for React, Next.js, and WordPress where the implementation differs significantly.