What it means
The server is temporarily unable to handle the request, due to overload or maintenance. Retry-After may say when to try again.
Common causes
- Planned maintenance
- Server overloaded or out of workers
- Autoscaling not caught up, or dependency outages
How to fix it
As a client or visitor
Retry later, honouring Retry-After.
As the site or API owner
Send Retry-After during maintenance, scale capacity, and shed load gracefully. Search engines treat short 503s as temporary.
Example response
HTTP/1.1
HTTP/1.1 503 Service Unavailable
Date: Tue, 07 Oct 2025 09:30:00 GMT
Server: nginx
Retry-After: 120
Content-Type: application/problem+json
{
"type": "about:blank",
"title": "Service Unavailable",
"status": 503,
"detail": "Down for maintenance until 02:00 UTC."
}Specification
FAQ
› Is 503 good for maintenance pages?
Yes. Return 503 with Retry-After; search engines then keep the page indexed instead of treating it as gone.
› 503 vs 500?
503 says the outage is temporary and expected to recover; 500 is an unexpected failure.