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Fixing the 'Not a Valid JSON Response' Error in WordPress

15 threads Sep 25, 2025 Core → Fixing wordpress

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If you've encountered the frustrating "An error occurred. The response is not a valid JSON response" message while trying to save a post, update a widget, or use the block editor, you're not alone. This is a common WordPress error that can halt your workflow. This guide will explain what this error means and walk you through the most effective solutions to resolve it.

What Does the "Not a Valid JSON Response" Error Mean?

This error occurs when WordPress sends a request to your server (for example, to save your work) but receives a response that isn't in the correct format. Instead of the expected JSON data, the server might be returning a PHP error, a blank page, or an HTML message. The block editor and other modern parts of WordPress rely on this JSON communication, so when it fails, you see this error.

Common Causes and Their Solutions

Based on community reports, this issue is typically caused by server-side configuration problems. Here are the most common culprits and how to fix them.

1. Check Your Permalinks

Incorrect permalink (URL) structure is a frequent cause. A simple reset often resolves the issue.

  • Go to your WordPress dashboard.
  • Navigate to Settings > Permalinks.
  • Simply click the "Save Changes" button without making any changes. This refreshes the rewrite rules.

2. Investigate Plugin or Theme Conflicts

A plugin or your theme might be interfering with the communication between WordPress and the server.

  • Disable All Plugins: Temporarily deactivate all your plugins. If the error disappears, reactivate them one by one to identify the problematic one.
  • Switch to a Default Theme: Temporarily switch to a standard WordPress theme like Twenty Twenty-Four. If this fixes the issue, the problem lies with your original theme.

3. Examine Server Error Logs

The most definitive way to find the root cause is to check your server's error logs. The exact error message logged there will point you directly to the problem.

  • Access your error logs through your hosting provider's control panel (e.g., cPanel). Look for a section called "Error Logs," "Logs," or "Metrics."
  • If you cannot find them, contact your hosting support and ask for the PHP error logs related to your website for the time the error occurred.

4. Enable WordPress Debugging

If you can't access the server logs, you can enable WordPress debugging to display errors on your site. Warning: Only do this on a staging site or temporarily on a live site, as it may reveal sensitive information to visitors.

  • Using an FTP client or your host's file manager, access your site's root directory and open the wp-config.php file.
  • Look for the line that says define('WP_DEBUG', false);.
  • Replace it with the following lines: 
    define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);
    This will create a debug.log file in your /wp-content/ directory where errors will be written. Remember to revert these changes after troubleshooting.

5. Other Server-Related Checks

  • ModSecurity: Sometimes, a security module on your server (like ModSecurity) can block a legitimate request. Contact your hosting provider to check if this is the case.
  • PHP Memory Limit: Ensure your PHP memory limit is set to a sufficient value (e.g., 256M or 512M). Your hosting provider can assist with this.

By methodically working through these steps, starting with the simplest, you can identify and fix the cause of the "Not a Valid JSON Response" error and get back to managing your site smoothly.

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