523 is a Cloudflare-specific code. It means Cloudflare cannot contact the origin web server at all, typically because a network device between Cloudflare and the origin has no route to the origin's IP address.
The most common cause is an incorrect origin IP address in the DNS records at Cloudflare, for example after a move to a new server or when the hosting provider changed the address. Routing problems at the origin's network provider can cause it as well.
Example response
HTTP
HTTP/1.1 523 Origin Is Unreachable
Date: Fri, 06 Nov 2026 10:15:32 GMT
Content-Type: text/html; charset=UTF-8
Connection: close
X-Frame-Options: SAMEORIGIN
Referrer-Policy: same-origin
Cache-Control: private, max-age=0, no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Expires: Thu, 01 Jan 1970 00:00:01 GMT
Server: cloudflare
CF-RAY: 8f3a1b2c4d5e6f73-SJCSEO and redirect checking
Like other origin errors, 523 makes the site unreachable for visitors and crawlers. Compare the A and AAAA records at Cloudflare with the server's current IPv4 and IPv6 addresses.
Common causes and use cases
- The origin IP address in Cloudflare's DNS is wrong or outdated.
- An
AAAArecord points to an IPv6 address that the server does not use. - Routing or peering problems at the origin's hosting provider.