Fix WordPress JSON Response Error (Invalid JSON Error) – Beginner’s Guide

The “Not a valid JSON response” error in WordPress (often seen in the block editor) means WordPress tried to communicate with the server via JSON but didn’t get a proper reply. In practical terms, your browser sent data (like your post content) to the site’s REST API, but the server’s response was empty, broken, or not valid JSON. Mohsin from Mohsin Webs explains that this usually happens due to URL mismatches, permalink issues, or server rules blocking the response.

A laptop with code illustrates how the WordPress editor uses JSON over the REST API to communicate with the server. If that JSON communication fails (for example, due to a URL or server issue), you’ll see the invalid JSON response error.

Understanding the WordPress JSON Response Error

When editing a post or page in the Gutenberg Block Editor, WordPress constantly sends and expects JSON data from the server. If something interrupts this (like a misconfigured URL, SSL issue, or security block), the editor will show “Updating failed. The response does not conform to a valid JSON structure.”. In simple terms, the editor sent information to your WordPress REST API endpoint, but the reply wasn’t valid JSON (it could be empty, HTML, or an error). HubSpot explains that the block editor relies on this hidden JSON request, so any communication glitch triggers the message.

Common scenarios include: your site URLs changed or use HTTP/HTTPS inconsistently, your Permalinks or .htaccess file are broken, Another plugin / theme ( like Soledad ) might be causing a conflict with the REST API. Even a security firewall or low server memory can break the JSON response. WPBeginner notes that most often it’s a simple URL or permalink issue.

Common Causes of the JSON Error

• Site URL or HTTPS Mismatch: If your WordPress Address/Site Address (URL) settings (in Settings → General) use the wrong domain or mix http and https, the REST API call will fail. Mixed-content (some resources on HTTP, some on HTTPS) can confuse WordPress and trigger the JSON error.
• Broken Permalinks or .htaccess: A corrupt or outdated permalink setup prevents WordPress from building correct REST API URLs. It usually goes away with emptying permalinks and rebuilding the. htaccess file.
• Plugin or Theme Conflict: A poorly coded plugin (or theme like Soledad) might block or modify REST API responses. Disabling all plugins (or switching to a default theme) is a quick way to identify conflicts. Even sometimes just one new plugin can cause the issue.
• Firewall/Security Blocks: WordPress security plugins or server firewalls (mod_security, Cloudflare, etc.) can block the block editor’s REST calls. Temporarily deactivating them can reveal if they’re the culprit.
• Media Upload Issues: Uploading media via the Gutenberg blocks can also trigger this error. It sometimes helps to add media via the Media Library instead of directly in the editor (avoiding block upload glitches).
• Server Configuration (Timeouts, PHP Limits): If your server is slow or has low PHP memory/time limits, the REST call may time out (often a cURL 28 error). For example, Soledad’s developers note that REST API errors often trace back to server timeout issues. Upgrading PHP limits or changing hosts can resolve these.

Step-by-Step Fix: Resolving the Invalid JSON Error

Follow these steps in order. They start from the most common/simple fixes to the more advanced. Go to the Settings menu and select the General tab from your dashboard.

• Check WordPress URLs and SSL (HTTPS). Access the General section under Settings in your dashboard. Ensure both the WordPress Address (URL) and Site Address (URL) are correct and use https:// if your site has SSL. Mismatched or non-HTTPS URLs will break the JSON response. If you recently switched to HTTPS but still see “http” here, update them and save changes. If you don’t have SSL, install one (many hosts provide free Let’s Encrypt certificates) and then update the URLs.
• Refresh Permalinks and Regenerate .htaccess. Navigate to Settings → Permalinks. Without changing anything, click Save Changes. This compels WordPress to regenerate its permalink settings. Next, check your .htaccess file: connect via FTP or your host’s file manager, back up the file, then delete it. Now re-save the permalink settings again to create a new clean .htaccess.

WordPress Permalink Settings screen (Settings → Permalinks). Regenerating permalinks by clicking “Save Changes” and rebuilding the .htaccess file often fixes JSON errors caused by rewrite issues.

• Ensure HTTPS and Fix Mixed Content. A common cause is mixed HTTP/HTTPS content. Confirm in Settings → General (as above) that both URLs use https://. If you’ve just installed an SSL certificate, update any hard-coded links. You can install a plugin like Really Simple SSL to automatically fix mixed content. This ensures all scripts and images load securely, preventing confusion in the editor.
• Deactivate Plugins and Switch Theme. It’s Plugins / Installed Plugins, on both the left side select all plugins and deactivate them. Then try saving or updating your post. If the error disappears, reactivate plugins one by one until the error returns – the last plugin activated is the conflict. Pay special attention to SEO plugins, caching plugins, or any that interact with REST API. Likewise, switch to a default theme (e.g. Twenty Twenty-Three) via Appearance → Themes. If using the Soledad theme, deactivate it temporarily. Sometimes the theme itself or a theme-specific plugin can cause the issue. PenciDesign (Soledad’s developers) note that REST errors can stem from server timeouts or outdated theme files. Updating Soledad or using a default theme tests this.
• Check for Firewall/Security Issues. If you have a security plugin (Wordfence, Sucuri, etc.) or a server-level firewall (mod_security, Cloudflare WAF), temporarily disable it. As Rank Math suggests, firewalls can disrupt the block editor’s server connection. If deactivating resolves the problem, you might need to whitelist WP’s REST API endpoints or opt for a security plugin that is compatible with Gutenberg.
• Try the Classic Editor (as a test). Install and activate the Classic Editor plugin. Switch to the Classic Editor (Settings → Writing) and try editing a post there. If the Classic Editor works fine, it confirms the problem is with Gutenberg’s REST calls. Note this is a temporary workaround; ideally you want Gutenberg fixed. But using Classic can let you update content in the meantime.
• Upload Media via the Library. If the error occurs while adding an image or media, open Media → Add New and upload your file directly, instead of inserting it through a block. Then add it to the block from the media library. This can bypass certain block-specific upload issues.
• Enable WordPress Debug Log (Advanced). To get more clues, enable WordPress debugging. Add these lines to your wp-config.php:

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);

Then recreate the error and check wp-content/debug.log. The log may show specific errors (e.g. PHP errors, cURL timeouts) that explain the JSON failure. Only do this temporarily, and disable debugging when done.

• Increase PHP Limits and Timeout. Some JSON errors happen if PHP runs out of memory or hits a time limit. Try increasing your memory limit and max execution time in php.ini or wp-config.php (e.g. define('WP_MEMORY_LIMIT', '256M');). If you see a cURL error 28 (Connection timed out) in your logs or browser console, it means the server response is too slow. In that case, contact your host to raise the timeout or speed up your server.
• Consider Hosting and Performance. If the error persists, it may be time to look at your hosting environment. A good managed WordPress host will have optimized servers (proper SSL setup, PHP settings, no overzealous firewall) to avoid these issues. For example, Mohsin Webs often recommends Websouls Hosting (affiliate link) for reliable WordPress performance. Websouls’ WordPress plans come with fast servers and preconfigured SSL, reducing REST API errors. Additionally, use performance tools: SpeedOx (a caching/optimization plugin by Mohsin Webs) can greatly speed up your site. Caching pages and minifying assets with SpeedOx (or similar plugins) lowers server load and can prevent timeouts that cause JSON failures. A faster site with optimized resources is less likely to throw REST API errors.

Optimizing performance can prevent server timeouts that lead to JSON errors. Consider using SpeedOx (by Mohsin Webs) to cache and minify your site, and host on a reliable provider like Websouls to ensure smooth WordPress REST API communication.

If after all these steps the error still appears, you may need expert help. As a final resort, you can reach out to WordPress support forums or a developer. Mohsin Webs emphasizes that virtually all invalid JSON errors have a root cause (URL mismatch, plugin conflict, server rule) that can be found and fixed with patience

Conclusion and Tips

In summary, the “Invalid JSON Response” error is usually a site configuration issue. Key takeaways:

• Always start by checking your URLs (make sure WordPress and Site Address use the same HTTPS domain).
• Refresh permalinks and regenerate the .htaccess file.
• Deactivate plugins/themes to isolate conflicts, and try the Classic Editor if needed.
• Review security/firewall settings to ensure they aren’t blocking the editor.
• Improve site health: use caching (SpeedOx), update your theme (Soledad or others), and consider stable hosting (Websouls affiliate link).

By methodically going through these checks, you can diagnose and fix the JSON response error. Remember to keep backups before major changes. With the right fixes, the WordPress REST API will work smoothly again – and you can continue editing your site without interruptions.

FAQs

1. WordPress mein “Invalid JSON response” error kyun aati hai?
Yeh error tab hoti hai jab WordPress server se sahi JSON data receive nahi kar pata — usually kisi URL, SSL, ya plugin conflict ki wajah se.

2. Kya permalink settings ko save karna is problem ko fix kar sakta hai?
Haan, Settings → Permalinks par jaake “Save Changes” karne se permalinks refresh ho jate hain jo kaafi baar yeh issue resolve kar dete hain.

3. Kya plugin conflict bhi JSON error ka reason ho sakta hai?
Bilkul. Kisi plugin ki wajah se REST API block ho sakta hai, isliye sab plugins deactivate karke phir ek ek karke activate karna helpful hota hai.

4. Agar SSL install kiya ho to URL ka HTTPS hona zaroori hai?
Haan, agar aapka site SSL use karta hai to WordPress Address aur Site Address dono https:// se start hone chahiye.

5. Agar koi theme (jaise Soledad) issue kar rahi ho to kya karen?
Theme ko temporary deactivate karke default theme (jaise Twenty Twenty-Three) lagayein. Agar problem solve ho jaye to theme ya uske plugin update karein ya support se contact karein.

Sources: Authoritative guides and documentation from HubSpot blog.hubspot.com, WPBeginner wpbeginner.com, Rank Math rankmath.com, WPZoom wpzoom.com, and Soledad theme support pencidesign.ticksy.com inform these steps. They emphasize URL/permalink checks, disabling conflicts, and server configuration as proven solutions.