What it means
Cloudflare-specific: Cloudflare cannot reach the origin, typically because of DNS or routing problems.
Common causes
- Wrong origin IP in DNS records
- Origin network is down
- Changed hosting without updating DNS
How to fix it
As a client or visitor
Retry later.
As the site or API owner
Verify the A/AAAA/CNAME records in Cloudflare DNS point to the current origin.
Example response
HTTP/1.1
HTTP/1.1 523 Origin Is Unreachable
Date: Tue, 07 Oct 2025 09:30:00 GMT
Server: nginx
Content-Length: 0Specification
Not in the IANA registry; used by Cloudflare. Cloudflare
FAQ
› What is the most common 523 cause?
A DNS record still pointing to an old server IP after migration.
› 523 vs 521?
523: the origin address is unreachable. 521: it is reachable but refuses connections.