523 Origin Is Unreachable

Cloudflare could not reach the origin at all, usually a routing or DNS problem.

Unofficial code. 523 is used only by Cloudflare. It is not in the IANA registry or any HTTP standard, and other software may give the number a different meaning or none.

Code: 523
Reason phrase: Origin Is Unreachable
Class: 5xx Server error
Used by: Cloudflare
Cacheable by default: No

What it means

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

Usual causes. A wrong or changed origin IP address in the DNS records, or a network routing fault.

What to do. Correct the origin IP in the DNS settings.

How clients and crawlers treat it

Google Search. Googlebot sees the 5xx code Cloudflare sends and treats it like any server error: it slows down crawling, and URLs that keep failing are eventually dropped from the index. 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/1.1 523 Origin Is Unreachable
Content-Type: text/plain; charset=utf-8

Origin Is Unreachable

Related codes

All status codes · All 5xx codes

Names and numbers from the IANA HTTP Status Code Registry (this code is not in it). Google Search behaviour as documented by Google Search Central.