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infoWordPress Core•apiREST APIsystem_updateUpdatelooploopbackschedulecron•labelCommon•warningModerate

Loopback request failed

WordPress sends an internal HTTP request to test its own functionality. The request fails when the server fails to reach the site address, when PHP stops the process, or when network rules block the call. The failure stops health checks, WP‑Cron, REST API and automatic updates.

The error appears in Site Health, in admin notices and in log files. It signals a breakdown in the communication loop that WordPress relies on for background tasks.

Symptoms

[dashicons-warning]
Site Health warning
Site Health shows a warning that the site could not complete a loopback request.
[dashicons-clock]
WP‑Cron not running
Scheduled events do not fire, causing missed backups or updates.
[dashicons-admin-tools]
REST API errors
Block editor displays REST API error messages such as cURL error 28.
[dashicons-update]
Automatic updates fail
Core, plugin or theme updates stop because WordPress cannot reach its own server.

Common Causes

Outdated cURL or timeout
cURL version is old or timeout is too low, causing the internal request to abort.
PHP limits
Memory limit or max execution time is low, preventing the loopback from completing.
Mismatched Site URL
Site URL or Home URL contains a typo or wrong protocol, so WordPress builds an invalid loopback URL.
Firewall or ModSecurity
Outbound HTTP requests to localhost are blocked by firewall rules or security modules.
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