HTTP 503 – Service Unavailable
The server is not ready to handle the request, often due to maintenance or overload.
Common use case
Used for planned maintenance windows or when a server is deliberately shedding load, typically paired with a Retry-After header.
Example
HTTP/1.1 503 Service Unavailable
Retry-After: 120
History
Part of HTTP/1.0 (RFC 1945, 1996).
Did you know?
Search engines generally won't deindex a page that returns 503 during a maintenance window, as long as it comes with a Retry-After header - unlike a 404 or 500, it's understood as temporary.