HTTP 503 Service Unavailable

Server error code, RFC 9110, section 15.6.4

What it means

The server cannot handle the request right now, due to overload or maintenance, and expects to be back after a while.

A real response

This is the request and the answer our test server gave when we asked it to return 503.

GET /c/503 HTTP/1.1
Host: example.com

HTTP/1.1 503 Service Unavailable
Date: Sat, 14 Nov 2026 10:00:00 GMT
Content-Type: text/html; charset=utf-8
Retry-After: 120
Content-Length: 11

<p>demo</p>

If you run the site

Use 503 for planned maintenance, with a Retry-After header with seconds or a date. Because 503 says the problem is temporary, it is the right code for a maintenance page; a maintenance page that answers 200 or 404 tells clients the wrong thing.

If you are a visitor

Try again later. If the site announced maintenance, wait for it to finish.

A common mistake

Showing a maintenance page with status 200.

Registered in the IANA HTTP Status Code Registry as Service Unavailable, defined in RFC 9110, section 15.6.4.

This is an independent guide. It is not connected with the IETF, IANA, any browser maker or any company named here. Meanings were checked against the RFC texts on 14 November 2026. Responses shown were recorded on 14 November 2026 from a small test server on the author's own computer.