508 Loop Detected

The server found an infinite loop while processing a WebDAV request.

Code: 508
Reason phrase: Loop Detected
Class: 5xx Server error
Defined in: RFC 5842 section 7.2
Cacheable by default: No

What it means

Server error: the request may be fine, but the server failed to carry it out.

Common causes. Bindings that refer back to themselves.

What to do. Fix the loop in the WebDAV structure.

How clients and crawlers treat it

Google Search. Googlebot treats 5xx responses as a sign of trouble and temporarily slows its crawl rate. Already indexed URLs are kept at first, but are dropped if the errors continue. Source: Google Search Central, How HTTP status codes, and network and DNS errors affect Google Search.

Caching. Not cacheable by default (RFC 9110 section 15.1 does not list it). A cache stores it only when the response says so with Cache-Control or Expires.

Example response

HTTP/1.1 508 Loop Detected
Content-Type: text/plain; charset=utf-8

Loop Detected

How to send 508

nginx

location /example {
    return 508;
}

Apache (.htaccess)

RewriteEngine On
RewriteRule ^example$ - [R=508,L]

PHP

http_response_code(508);
echo 'Loop Detected';
exit;

Node.js

res.writeHead(508, { 'Content-Type': 'text/plain' });
res.end('Loop Detected');

Python (Flask)

# in a view function
return 'Loop Detected', 508

Change the paths to suit. In nginx, add_header needs always to apply to error responses.

Related codes

All status codes · All 5xx codes

Names and numbers from the IANA HTTP Status Code Registry. Google Search behaviour as documented by Google Search Central.