# 409 Conflict

> The request conflicts with the current state of the target resource.

Source: https://apiguide.dev/status-codes/409
Class: client-error
Defined in: RFC 9110, Section 15.5.10 <https://www.rfc-editor.org/rfc/rfc9110.html#section-15.5.10>
Updated: 2026-10-14

## What does HTTP status code 409 mean?

The 409 Conflict status code indicates that the request cannot be completed because it conflicts with the current state of a resource (e.g. database constraints).

## When to use it in APIs

Use 409 for optimistic concurrency conflicts (stale version tags), duplicate unique keys (like email address collisions), or a retry that arrives while the original request with the same `Idempotency-Key` is still in flight. A key reused with a different payload is 422, per the idempotency key draft.

## How it compares to other codes

* **422 Unprocessable Content**: Used for general field-level business validation. 409 is reserved for state-driven conflicts.