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.
What you get
- Code and configuration patterns for LCP, CLS and INP
- Third-party script management strategies
- Notes for React, Next.js and WordPress
- Provided on request through the contact form
Who it's for: Front-end developers and technical SEOs implementing Core Web Vitals improvements.
What this guide is for
The Core Web Vitals Fix Guide explains what to fix. The Code Fix Reference shows how, with implementation patterns for the issues that appear most often. It is a developer-focused PDF, framework-agnostic, with notes for React, Next.js and WordPress where the implementation differs.
What it covers
LCP fixes: responsive image markup with width and height attributes, next-generation image formats in HTML and WordPress, preload hint syntax for hero images, server-side rendering considerations, and server cache-header configuration for nginx and Apache, which affects LCP indirectly through response time.
CLS fixes: aspect-ratio CSS for images and iframes, reserved space for ad slots, font-display swap, and ways to control layout shifts from dynamically injected elements. Each pattern has a before-and-after code comparison.
INP fixes: deferring non-critical JavaScript, splitting long tasks with scheduler.postTask or setTimeout, passive event listeners and input debouncing. A third-party script section covers isolating analytics, chat widgets and marketing tags that create long tasks.
A closing testing checklist lists the tools to confirm each fix.
How to use it
Diagnose first: find the actual failing element or task with field data and a lab trace, then pick the matching pattern. Apply one change at a time and test it on a real mobile device or a throttled profile. Review third-party tags early, since they are a frequent cause of long tasks. After release, check field data over the following weeks instead of relying on a single lab score.
The guide is provided on request. Would you rather have this done for you? Fill out the form on our contact page, tell us about the business, and we will come back with a quote.
Who it is for
Front-end developers and technical SEOs who are implementing Core Web Vitals fixes and want working patterns in front of them.
Frequently asked questions
- How is it different from the Core Web Vitals Fix Guide?
- The Fix Guide helps you diagnose and prioritise. This reference shows the code and configuration patterns for the fix.
- Will these patterns work in any framework?
- The patterns are framework-agnostic, with notes where React, Next.js or WordPress need a different approach.
- Why do third-party scripts matter?
- Analytics, chat and marketing tags can create long tasks that delay interactions, which hurts INP, so they deserve their own review.
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