What class of response is HTTP 409?

HTTP 409 is a 4xx Client Error response. These indicate a client-side error.

How do I fix HTTP 409 Conflict?

HTTP 409 is a client error. Verify the request URL, method, headers, and body are correct. Consult the API documentation for the endpoint.

Is HTTP 409 an error?

Yes, HTTP 409 is an error — specifically a 4xx Client Error code.

HTTP 409 Conflict: What It Means and When You See It

Quick Answer

HTTP 409 Conflict means the request conflicts with the current state of the server — for example, trying to create a resource that already exists.

When HTTP 409 Is Returned

HTTP 409 Conflict means the request cannot be completed because of a conflict with the current state of the resource. Common examples: creating a user with an email that already exists, updating a record with an outdated version (optimistic locking), concurrent edits to the same resource, and violating a unique constraint in the database. The response body typically explains what conflicted and how to resolve it.

Implementing 409 in APIs

Use 409 when a uniqueness constraint fails: if (await db.users.findByEmail(email)) return res.status(409).json({ error: "Email already in use" }). For optimistic locking: check the version or ETag before updating, return 409 if the record was modified by another request. The client should read the current state, resolve the conflict, and retry. Express.js: res.status(409).json({ error: "Conflict", field: "email" }).

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Frequently Asked Questions

Related Values

100

HTTP 100 Continue means the server has received the request headers and the client should proceed to send the request body. It is an interim response used to inform the client to continue.

101

HTTP 101 Switching Protocols indicates the server is switching to the protocol specified in the Upgrade header field. Commonly used when upgrading to WebSocket connections.

200

HTTP 200 OK is the standard success response. The request has succeeded and the server has returned the requested resource in the response body.

201

HTTP 201 Created means the request succeeded and a new resource was created as a result. The Location header typically points to the new resource URL.