HTTP 428 – Precondition Required
The origin server requires the request to be conditional, to avoid lost update conflicts.
Common use case
Forces clients to send an If-Match header before updating a resource, preventing the classic "lost update" problem where two clients overwrite each other's changes.
Example
HTTP/1.1 428 Precondition Required
History
Standardised in RFC 6585 (2012), one of a small batch of new codes added to plug practical gaps developers had been working around for years.
Did you know?
It effectively makes conditional requests mandatory rather than optional - a stricter sibling of 412 Precondition Failed.