HTTP 409 Conflict

Client error code, RFC 9110, section 15.5.10

What it means

The request clashes with the current state of the thing. For example, creating something that already exists, or saving over a version that changed.

A real response

This is the request and the answer our test server gave when we asked it to return 409.

GET /c/409 HTTP/1.1
Host: example.com

HTTP/1.1 409 Conflict
Date: Sat, 14 Nov 2026 10:00:00 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 11

<p>demo</p>

If you run the site

Use 409 when the user could fix the clash and try again, and say in the body what clashes: a duplicate user name, an edit based on an old version. For edits, send an ETag and let clients send If-Match; a failed match is answered with 412 (Precondition Failed), which this site does not cover.

If you are a visitor

Read the message: it usually says what is already there. Change your request and send it again.

A common mistake

Returning 500 for duplicates, which hides a user mistake as a server fault.

Registered in the IANA HTTP Status Code Registry as Conflict, defined in RFC 9110, section 15.5.10.

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.