DevKits
409

Conflict

4xx Client Error

Last updated:

The request conflicts with the current state of the resource.

Description

Common for concurrent modification: two clients try to update the same resource, and the second update is rejected. Also used for uniqueness violations (e.g. registering an email that already exists).

When to use

Return 409 for optimistic locking failures, duplicate key errors, or state-machine violations.

Specification

RFC 9110 §15.5.10

Examples

HTTP response
HTTP/1.1 409 Conflict
Content-Type: application/json

{"error":"Conflict"}
Node.js (Express)
res.status(409).json({ error: "Conflict" });
Go (net/http)
w.WriteHeader(http.StatusConflict)
Python (Flask)
return jsonify({"error": "Conflict"}), 409

Related status codes

412

Precondition Failed

A precondition given in the request headers (e.g. If-Match) evaluated to false.

422

Unprocessable Entity

The request is well-formed but contains semantic errors and cannot be processed.

All 4xx codes

400 Bad Request401 Unauthorized403 Forbidden404 Not Found405 Method Not Allowed406 Not Acceptable408 Request Timeout409 Conflict410 Gone411 Length Required412 Precondition Failed413 Payload Too Large414 URI Too Long415 Unsupported Media Type418 I'm a teapot422 Unprocessable Entity425 Too Early428 Precondition Required429 Too Many Requests431 Request Header Fields Too Large451 Unavailable For Legal Reasons