HTTP 409 — Conflict
HTTP 409
Conflict
The request cannot be completed because it clashes with the current state of the resource.
What 409 actually means
The request is well formed and you are allowed to make it, but doing so right now would break something. The two classic cases are a duplicate — registering an email address that already exists — and a lost update, where two people edited the same record and the second write would silently discard the first. A 409 is a request that could succeed later or in a different order, which distinguishes it from 400 and 422.
Common causes
- A unique constraint violated: username, email or slug already taken
- Optimistic concurrency failure — the `If-Match` ETag no longer matches
- Two edits to the same resource landing at once
- Trying to delete something other records still depend on
- A version control style conflict in a sync API
If you're just trying to view the page
- Reload the page to get the current version, then reapply your change
- If it is a signup or rename, choose a different value — something already uses the one you picked
- Check whether someone else edited the same item while you had it open
If it's your site
- Say what conflicted in the response body; "Conflict" alone forces the client to guess
- Use ETags with `If-Match` so conflicts are detected rather than silently overwriting
- Distinguish "already exists" from "version mismatch" with a machine-readable error code
- Where safe, make the operation idempotent so a retry succeeds instead of conflicting
Reference
- Status code
- 409
- Reason phrase
- Conflict
- Category
- 4xx — Client Error
- Defined in
- RFC 9110 §15.5.10
Common questions
- What does HTTP 409 mean?
- The request cannot be completed because it clashes with the current state of the resource. The request is well formed and you are allowed to make it, but doing so right now would break something. The two classic cases are a duplicate — registering an email address that already exists — and a lost update, where two people edited the same record and the second write would silently discard the first.
- How do I fix a 409 error?
- Reload the page to get the current version, then reapply your change
- Is 409 a client error or a server error?
- 409 is in the 4xx range, which means client error. The request itself was the problem, so retrying it unchanged will usually return the same code.
Related pages
- 404 Not Found The server is reachable and working, but there is nothing at the address you ask
- 403 Forbidden The server understood the request and is refusing to allow it, and logging in wi
- 401 Unauthorized You need to authenticate, and either you did not or your credentials were reject
- 429 Too Many Requests You have sent more requests than the service allows in a given period.
- 400 Bad Request The server could not understand the request because something about it is malfor
- 413 Content Too Large The request body is bigger than the server is willing to accept.
- 422 Unprocessable Content The request is well-formed and understood, but the data in it fails the rules.
- 405 Method Not Allowed The URL exists, but it does not accept the HTTP method you used.
- 415 Unsupported Media Type The server will not accept the format of the body you sent.
- 408 Request Timeout The server gave up waiting for the client to finish sending its request.
- 410 Gone The resource was deliberately removed and is not coming back, and there is no fo
- 451 Unavailable For Legal Reasons The content is blocked because of a legal demand — a court order, takedown notic