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412 4xx RFC 9110 §15.5.13

Precondition Failed

A precondition (If-Match, If-Unmodified-Since) in the request headers failed.

What HTTP 412 means

RFC 9110 §15.5.13. Used in optimistic concurrency control: the client sends If-Match: <etag>, and 412 means the resource has changed since.

Typical causes

  • If-Match header doesn't match current ETag
  • If-Unmodified-Since precondition failed