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Troubleshooting WebP Display Issues with WP Rocket and Caching Plugins

17 threads Sep 9, 2025 Plugin → Converter for media – optimize images | convert webp & avif

Content

Many users of the 'Converter for Media – Optimize images | Convert WebP & AVIF' plugin report issues where WebP images fail to display after installing or configuring a caching plugin, particularly WP Rocket. This guide explains why this conflict happens and provides the most common solutions to get your WebP images serving correctly.

Why Do Caching Plugins Cause WebP Issues?

The 'Converter for Media' plugin typically serves WebP images using server-level rewrite rules (in an .htaccess file for Apache or a configuration snippet for Nginx). These rules check the browser's acceptance of WebP and serve the appropriate image format on the fly.

Page caching plugins, like WP Rocket, create static HTML copies of your pages to serve to visitors. A potential conflict arises when this static cache is generated before the server rules have a chance to run. The cached page might contain direct links to the original JPEG/PNG files, locking them in place and bypassing the dynamic WebP conversion process.

Common Symptoms

  • WebP images were working but stopped after enabling a caching plugin.
  • Image inspection in the browser shows .jpg or .png files are still loading, even in WebP-supported browsers.
  • WP Rocket's 'WebP Compatibility' add-on reports: "We have not detected any compatible WebP plugin!".
  • Lazy loaded images further down the page do not convert to WebP, while the first images do.

How to Troubleshoot and Resolve the Conflict

1. Clear All Caches

This is always the first step. After configuring the WebP converter, you must clear your page cache, browser cache, and any other server-level caches (like Varnish or Redis). This ensures that new, uncached page requests are made, allowing the server rules to properly generate and serve WebP images before the page is cached again.

2. Configure WP Rocket Correctly

If you are using WP Rocket, its official documentation states that you should NOT enable its 'WebP Compatibility' add-on if your WebP plugin uses .htaccess rules to serve images. The 'Converter for Media' plugin uses this method by default. Enabling WP Rocket's WebP feature in this scenario can create a conflicting double cache. Ensure this add-on is disabled in WP Rocket's settings.

3. Enable the "Force Redirections" Option

Within the 'Converter for Media' settings, navigate to the 'Advanced' section. Enable the option labeled "Force redirections to WebP for all domains". This can help resolve issues where lazy load functionality or complex caching layers interfere with the standard redirection logic.

4. Verify Server Configuration

For the plugin's rewrite rules to work, the server must be configured correctly.

  • Apache: Ensure the rules generated by the plugin are present in your .htaccess file and that Apache's mod_rewrite module is enabled.
  • Nginx: The rules provided in the plugin's FAQ must be manually added to your server's Nginx configuration file. Unlike .htaccess, these rules cannot be added automatically.

After adding configuration for Nginx, you must reload the Nginx service.

5. Check for CDN or Proxy Caching

If you use a CDN (like Cloudflare) or a proxy cache (like Varnish), they might be serving cached JPEG versions of your images. You must configure these services to respect the origin server's caching headers and, most importantly, purge their caches after making any changes to your image serving setup.

6. Test with a Default Theme and Other Plugins Disabled

To rule out conflicts with your theme or other plugins, temporarily switch to a default WordPress theme (like Twenty Twenty-Four) and disable all plugins except 'Converter for Media' and your caching plugin. If WebP images serve correctly, reactivate your themes and plugins one by one to identify the source of the conflict.

What Doesn't Work (And Why)

Some users ask if they can change the directory where WebP files are stored to the standard uploads folder to satisfy certain cache plugins. Based on sample threads, the 'Converter for Media' team has indicated this is not possible. The plugin's architecture relies on storing converted images in a separate webp directory for its rewrite rules to function correctly.

By methodically working through these steps, most users can successfully resolve conflicts between the 'Converter for Media' plugin and their chosen caching solution, resulting in a faster website with properly served next-generation images.

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