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Troubleshooting Common WebP Express Plugin Conflicts and Compatibility Issues

24 threads Sep 16, 2025 Plugin → Webp express

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WebP Express is a powerful tool for serving next-generation WebP images on your WordPress site. However, users often encounter issues when trying to make it work alongside other popular plugins and services. Based on community reports, this guide covers the most common compatibility problems and their solutions.

Common Compatibility Issues and Solutions

1. Caching Plugins (WP Rocket, W3 Total Cache)

Problem: WebP images not serving properly when page caching is active. Users report seeing only original JPEG/PNG files when logged out (using cached pages).

Solution: The WebP Express team recommends using the "Replace tags with <picture> tags" HTML alteration method, which is fully compatible with page caching. Avoid the "Replace image URLs" method, as it does not work with cached pages. Several users have confirmed this configuration works flawlessly with WP Rocket.

2. CDN and Offload Media (WP Offload Media, S3 Buckets)

Problem: WebP files are generated but not uploaded to or served from remote storage buckets (like AWS S3 or Digital Ocean Spaces). Tests involving reading from the bucket often fail.

Solution: This typically occurs because the offload plugin's hooks are not triggered during WebP Express's test operations. Ensure your offload plugin is correctly configured to handle media operations. You may need to check if the generated WebP files are being synced to your bucket. Manual configuration or specific setup guides for your storage provider may be necessary.

3. Image Optimization Plugins (Smush, ShortPixel)

Problem: Conflicts or questions about the benefits of running WebP Express alongside other image optimizers.

Solution: WebP Express can generally work alongside plugins like Smush. Smush handles image compression and optimization, while WebP Express focuses specifically on WebP conversion and delivery. There is no inherent conflict, but it's important to configure them correctly to avoid duplicate processing. Ensure Smush is not also set to deliver WebP images to prevent any delivery-level conflicts.

4. AMP Plugins (AMPforWP, Official AMP)

Problem: WebP images do not appear on AMP pages. Some users report validation errors because the <picture> tag is not allowed in AMP HTML outside of a <noscript> tag.

Solution: The "Varied image responses" (redirection) method is the recommended approach for AMP compatibility, as it does not alter the HTML and therefore avoids AMP validation errors. The HTML alteration methods are not AMP-compliant. If you must use HTML alteration, you may need to disable WebP Express on AMP pages or seek a specific AMP compatibility extension.

5. Security and Firewall Plugins (All In One WP Security)

Problem: Receiving 403 Forbidden errors when trying to serve WebP images, often linked to enabled firewall rules (like the 6G Blacklist).

Solution: This is usually caused by security rules that block the specific URL patterns or query strings used by WebP Express. Test by temporarily disabling the firewall rules to confirm. If the problem is resolved, you will need to add an exception for WebP Express's rules in your security plugin's settings. The plugin's author has noted that recent versions have addressed some mishaps that could cause these conflicts.

6. Server Configuration (exec() function, .htaccess)

Problem: Conversion fails on managed hosting where the exec() function is disabled or where .htaccess rules are not processed.

Solution: You do not need exec() for all conversion methods. Try using a "local" converter like Vips, Gd, Imagick, or Gmagick in the WebP Express settings. If your server does not process .htaccess files (common on NGINX or some configured Apache servers), you will need to manually add the provided redirection rules to your server's main configuration file for the "Varied image responses" method to work.

General Troubleshooting Tips

  • Use the Test Features: WebP Express includes thorough debugging tools. Use the "Test" buttons for converters and append ?debug to an image URL to get a detailed textual report of the conversion process.
  • Check Your Mode: Many conflicts are resolved simply by switching between the "Varied image responses" and "Alter HTML" delivery methods. Test which one works best with your stack.
  • Clear All Caches: After changing settings, clear your WordPress cache, browser cache, and any CDN caches to see the changes take effect.

For more specific issues, checking the WebP Express GitHub repository for existing reports or to open a new issue is often the best course of action.

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