412 Precondition Failed

The 412 Precondition Failed HTTP status code indicates the requested action was not performed because a conditional test failed. This typically indicates the resource changed since the previous request to this resource, and the client should re-request the representation and try again.

Writing responses (origin servers)

If the request contains an If-Unmodified-Since or If-Match headers, parse each header header and return 412 Precondition Failed if the condition fails. The response payload may be a document describing the reasons for failure, the new state of the resource, and/or changes to the resource since the client's copy.

If the client is attempting to perform a safe request and the server merely needs to indicate there's no changes, without indicating an error, see 304 Not Modified instead.

Reading responses (user agents)

A 412 Precondition Failed indicates the resource changed between the last cache update and this request. The client needs to update the representation available, re-apply the changes, and try again.

See If-Unmodified-Since and If-Match for guidence on making these requests.

Overview table

Name

412

Message

412 Precondition Failed

Description

The conditional request failed.

Specification

RFC 7232: HTTP/1.1 Conditional Requests §4.2. 412 Precondition Failed

Example

HTTP/1.1 412 Precondition Failed
Content-Type: text/plain

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