HTTP 409 Conflict — Resolving Resource State Conflicts

Overview

HTTP 409 Conflict indicates the request conflicts with the current state of the server resource, common in concurrent editing and version control scenarios.

Key Details

• 409 signals that the request cannot be completed due to a conflict with the resource's state
• Common in RESTful APIs when two clients try to modify the same resource simultaneously
• Often used with ETags and If-Match headers for optimistic concurrency control
• The response body should describe the conflict so the client can resolve it
• Different from 412 Precondition Failed which is about conditional request headers

Common Causes

• Two users editing the same document simultaneously (edit conflict)
• Trying to create a resource that already exists (duplicate key)
• Version mismatch — client has stale data and tries to update
• Database unique constraint violation surfaced through the API
• Git-like merge conflict in collaborative editing systems

Steps

1. 1Read the response body for details about what conflict occurred
2. 2Fetch the latest version of the resource with a fresh GET request
3. 3Merge your changes with the current state and retry the request
4. 4Use If-Match with ETag headers for optimistic concurrency control
5. 5Implement retry logic with exponential backoff for automated systems

Tags

More in 4xx Client Error

Frequently Asked Questions