HTTP 409 — Conflict
4xx Client Error
What it means
The request conflicts with the current state — a duplicate unique key, or an edit based on a stale version.
What to do about it
Fetch the current state and retry, or implement optimistic concurrency with ETag and If-Match.
Where it sits
409 belongs to the 4xx family: The request contains something the server will not or cannot process. The fix is normally on the client side.
HTTP/1.1 409 ConflictChecking it yourself
# see the status code and headers only
curl -sI https://example.com/path
# follow redirects and print each hop
curl -sIL -o /dev/null -w "%{http_code} %{url_effective}\n" https://example.com/path
# JavaScript
const r = await fetch(url);
console.log(r.status, r.statusText);How this code behaves
| Cacheable by default | No — caches must not store this response unless explicit cache headers permit it. |
| Safe to retry | No. Retrying an identical request will produce the same result — the request itself must change. |
| Effect on search indexing | No direct effect. |
Returning 409 correctly
# nginx
return 409;
# Express
res.status(409).json({ error: 'Conflict' });
# Go
w.WriteHeader(409)
# Python (Flask)
return jsonify(error='Conflict'), 409;Frequently asked questions
What does HTTP 409 mean?
The request conflicts with the current state — a duplicate unique key, or an edit based on a stale version.
How do I fix a 409 error?
Fetch the current state and retry, or implement optimistic concurrency with ETag and If-Match.
Is 409 a client or server problem?
A client problem by definition — the request needs to change. That said, a 4xx can still be the server’s fault if it is misconfigured and rejecting valid requests.