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infoWordPress Core•apiREST APIerrorerrorerrorwp_errorcodejsonsettingsserver_configuration•labelCommon•warningModerate

WP_Error: Invalid JSON response body

WordPress expects a JSON payload from its REST API. When the server sends HTML, an empty body, or a 403 page, the response fails to parse as JSON. This mismatch stops the editor from saving content and shows an error.

The problem usually stems from server settings, URL mismatches, rewrite rules, or code that outputs warnings before the JSON data.

Symptoms

[dashicons-warning]
Editor error banner
Gutenberg shows a red banner stating the response is not a valid JSON response.
[dashicons-admin-site]
HTML response in network tab
Browser network panel shows the REST request returning HTML or an empty body.
[dashicons-admin-generic]
Console WP_Error message
JavaScript console logs WP_Error: Invalid JSON response body.

Common Causes

Mismatched URLs
Site URL and Home URL use different protocols or domains, causing requests to hit the wrong address.
Broken permalinks
Rewrite rules send the API request to a 404 page or HTML output.
Plugin or theme output
PHP warnings, notices, or stray echo statements prepend HTML before the JSON payload.
Security or firewall block
ModSecurity or WAF rules block application/json requests and return a forbidden HTML page.
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