A Basic Guide To Use Claude.ai To Improve Page Speed for Your WordPress Website

Page speed with SEO rankings, provides a better user experience, and helps increase conversion rates. A slow website costs you visitors, rankings, and revenue. This guide walks you through auditing your site with Google’s free PageSpeed Insights tool and using AI to generate the code fixes directly into your WordPress child theme – no developer required.

Why Page Speed Matters

• Better SEO Rankings – Google uses Core Web Vitals as a direct ranking signal.
• Lower Bounce Rate – 53% of mobile visitors will leave a page that takes more than 3 seconds to load.
• Higher Conversions – A 1-second improvement in load time can increase conversions by up to 7%.
• Better Mobile Experience – Mobile users on slower connections benefit the most from an optimized site.
• Competitive Advantage – A fast site immediately sets you apart.

Optional Plugin: WP Rocket

WP Rocket is the most popular premium WordPress performance plugin and can resolve many PageSpeed issues automatically – without touching any code. It is a great starting point before making manual changes to your functions.php file.

What WP Rocket handles automatically:

• Page caching and browser caching
• GZIP compression
• Minification of CSS, JavaScript, and HTML
• Deferring non-critical JavaScript
• Lazy loading images and videos
• Database optimisation
• DNS prefetching and preloading
• Preloading the cache

How to install: Purchase WP Rocket from wp-rocket.me, upload the plugin zip via WordPress Admin → Plugins → Add New → Upload Plugin, activate it, and run your PageSpeed audit again. Many failed checks will resolve automatically.

Note: If you install WP Rocket, check which issues it resolves before adding manual code to your functions.php – avoid duplicating fixes, as this can cause conflicts. You can add this to the prompt for defining the fix ( for example, include, I am using the WP Rocket plugin) – this will help it not only output the best Functions.php file, but also give you options to better utilize WP Rocket.

Quick List of Steps – If You Know What You’re Doing

1. Go to pagespeed.web.dev and run an audit on your website
2. Note every failed and needs-improvement check in the results
3. (Optional) Install WP Rocket and re-run the audit to see what it resolves automatically
4. For each remaining failure, paste it into Claude and ask for the functions.php fix
5. Copy your existing functions.php and ask Claude to merge both into one clean file
6. Replace your child theme’s functions.php with the merged file
7. Test all website functionality thoroughly
8. Re-run the audit, verify your score improvement, and repeat for the remaining issues

The Detailed Step-by-Step Guide

Step 1 – Run Your Audit on PageSpeed Insights

Go to pagespeed.web.dev, enter your website URL, and click Analyze.

Google will test both the mobile and desktop versions of your page and return a score from 0–100 across four categories:

• Performance – Speed and load efficiency (this is your primary target)
• Accessibility – How usable your site is for all users
• Best Practices – Security, modern code standards
• SEO – On-page technical SEO signals

What to aim for: A Performance score of 95+ on desktop and 80+ on mobile. Anything below 60 is considered poor and needs urgent attention.

Step 2 – Identify All Failed Sections

Scroll down past your score to the Opportunities and Diagnostics sections. This lists every failed or underperforming check on your page. Note each one – these are what you will be fixing.

Common failures on WordPress sites include:

• Eliminate render-blocking resources (undeferred CSS/JavaScript)
• Serve images in next-gen formats (WebP or AVIF)
• Properly size images (oversized media files)
• Reduce unused JavaScript or CSS
• Enable text compression (Gzip or Brotli)
• Leverage browser caching
• Minify CSS, JavaScript, and HTML
• Reduce server response times (TTFB – Time to First Byte)
• Avoid enormous network payloads
• Efficiently encode images

Step 3 – Send Each Failed Section to Claude for a Fix

For each failed check, copy the name and description from PageSpeed Insights and paste it into Claude. Ask Claude to generate the appropriate functions.php code to resolve that specific issue in WordPress.

Example prompt you can use:

“My WordPress site is failing the following PageSpeed Insights check. I am using the [Hub / Ave] theme with Visual Composer. Please generate the functions.php code for my WordPress child theme to fix this issue.

Failed check: Eliminate render-blocking resources

Description from PageSpeed Insights: Resources are blocking the first paint of your page. Consider delivering critical JS/CSS inline and deferring all non-critical JS/styles. Potential savings of 1,320 ms.

The following resources have a significant blocking time:

https://yourdomain.com/wp-content/themes/hub/css/style.css

https://yourdomain.com/wp-includes/js/jquery/jquery.min.js

Include as much detail from the PageSpeed report as possible – the check name, the description, the estimated saving, and any specific files or URLs it lists. The more detail you provide, the more targeted and accurate the generated code will be.

You can fix issues one at a time or batch multiple failures into a single prompt. Claude will output a ready-to-use code block you can copy directly into your child theme.

Tips for better results:

• Mention your theme name so Claude can account for theme-specific scripts
• Mention a page builder if you are using one, such as Elementor or Visual Composer, so Claude knows to exclude its scripts from deferral
• If a fix breaks something, describe what broke and ask Claude to adjust the code

 

Step 4 – Combine the New Code with Your Existing functions.php

Before making any changes to your live file, open your current functions.php and copy the entire contents. Then go back to Claude and paste it in alongside the new code it just generated, with the following prompt:

“Here is my current functions.php file:

[paste your existing functions.php contents here]

Please combine this with the new code you just generated into a single, clean functions.php file, making sure there are no duplicate functions, no conflicts, and the formatting is consistent throughout.”

Claude will output a single merged file ready to copy and paste. This is the safest approach – combining the files first means you are replacing your existing file with one complete, reviewed version rather than manually inserting code snippets in the right places.

Why this matters: Pasting new code into the wrong position in an existing functions.php file – for example, after a closing ?> tag or inside an existing function – is one of the most common causes of WordPress errors. Letting Claude merge and check the file eliminates that risk.

 

Step 5 – Update Your Child Theme’s functions.php File

Once Claude outputs the code, add it to the functions.php file in your child theme. Always edit the child theme – never the parent theme, as updates will overwrite your changes.

How to access your functions.php file:

• Via WordPress Admin: Go to Appearance → Theme File Editor → functions.php (select your child theme from the dropdown on the right)
• Via FTP/SFTP: Navigate to /wp-content/themes/[your-child-theme]/functions.php
• Via File Manager: Access through your hosting control panel and navigate to the same path above

⚠️ Important – Back Up Before Editing: Always create a full backup of your website before modifying any theme files. A syntax error in functions.php can take your site offline. If that happens, access your file via FTP and remove or correct the added code.

Paste the code Claude generated at the bottom of your functions.php file, above the closing ?> tag if one exists (most modern files do not have one).

 

Step 6 – Test All Website Functionality

After each change, thoroughly test your website before running another PageSpeed audit. Performance changes – especially JavaScript deferral – can sometimes break interactive elements, page builder layouts, or third-party plugins.

Testing checklist:

• All pages and layouts render correctly on desktop and mobile
• Navigation menus open, close, and link correctly
• Contact forms submit successfully and send emails
• Any sliders, carousels, or animations still work
• Visual Composer elements display as expected
• Any popups or lightboxes still trigger correctly
• WooCommerce checkout completes (if applicable)
• No JavaScript errors visible in the browser console (right-click → Inspect → Console)

If something breaks, return to Claude and paste a description of what is broken – Claude can update the code to exclude specific scripts or adjust the approach.

Step 7 – Re-Run PageSpeed Insights and Repeat

Once your testing passes, go back to pagespeed.web.dev, re-run the analysis, and confirm your score has improved. Then repeat Steps 2–5 for each remaining failed item until you have worked through the full audit list.

Note on image optimization: Some improvements – such as converting images to WebP format – cannot be handled through functions.php alone. For image conversion, use a plugin such as Imagify (it works well with the WP Rocket plugin) alongside your code changes.

This guide is intended as a practical starting point. Every WordPress site is different – your theme, plugins, and hosting environment will all affect which fixes apply and how much improvement you achieve. Work through the audit methodically and test after every change.