HTTP 409 Conflict

What Does HTTP 409 Mean?

HTTP 409 Conflict indicates that the request could not be completed because of a conflict with the current state of the target resource. The client should be able to resolve the conflict and resubmit the request.

HTTP 409 is commonly used in REST APIs for: version conflicts (optimistic locking), attempting to create a resource that already exists, conflicting concurrent modifications, and state machine violations (e.g., trying to publish an already-published article).

The response body should explain the conflict and ideally provide enough information for the client to resolve it. This status code is most useful in APIs with PUT operations where the client's version of a resource conflicts with the server's version.

Common Causes of 409 Conflict

The request conflicts with the current state of the resource. Common causes: editing a resource that was modified by another user (optimistic locking conflict), creating a resource with a duplicate unique key, and state transition violations.

The response should explain the conflict so the client can resolve it.

How to Fix 409 Conflict

Refresh the resource and retry with the updated version. For optimistic locking conflicts, re-read the resource, apply your changes to the latest version, and resubmit. For duplicate key errors, use a different identifier or check if the resource already exists.

Implement proper conflict resolution in your application's UI to guide users through resolving conflicts.

Related Status Codes

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