HTTP 409 Conflict

What does HTTP 409 mean?

The request conflicts with the current state of the resource. Typical in APIs: creating a user with an email that already exists, or updating a record that someone else changed in the meantime (optimistic locking with version numbers or ETags).

4xx Client error: The request has a problem the client can fix: wrong URL, missing credentials, bad data or too many requests.

Common causes of a 409 error

• Duplicate unique value (email, username, slug).
• Edit conflict between two clients.

How to fix 409 Conflict

• Fetch the latest version, merge the changes and retry.
• Show users a clear “already exists” message.

409 and SEO

Not relevant for web pages.

Example response

HTTP/1.1 409 Conflict

How to return a 409 response

Node.js (Express)

res.status(409).json({ error: 'Conflict' });

PHP

http_response_code(409);

Python (Flask)

return {'error': 'Conflict'}, 409

Go (net/http)

w.WriteHeader(409)

nginx

return 409;

Related status codes

• 412 Precondition Failed — A condition in the request headers (If-Match, If-Unmodified-Since) was not met.
• 422 Unprocessable Content — The request is well-formed but contains semantic errors.
• 201 Created — The request succeeded and a new resource was created.

Check which status code a URL returns with the HTTP header checker.