Warning

The Warning general HTTP header contains information about possible problems with the status of the message. More than one Warning header may appear in a response.

Warning header fields can in general be applied to any message, however some warn-codes are specific to caches and can only be applied to response messages.

Syntax

Warning: <warn-code> <warn-agent> <warn-text> [<warn-date>]

Directives

<warn-code>

A three-digit warning number. The first digit indicates whether the Warning is required to be deleted from a stored response after validation.

• 1xx warn-codes describe the freshness or validation status of the response and will be deleted by a cache after deletion.

• 2xx warn-codes describe some aspect of the representation that is not rectified by a validation and won't be deleted by a cache after validation unless a full response is sent.

<warn-agent>

The name or pseudonym of the server or software adding the Warning header (might be "-" when the agent is unknown).

<warn-text>

Advisory text describing the error.

<warn-date>

Optional. If more than one Warning header is sent, include a date that matches the Date header.

Warning codes

The HTTP Warn Codes registry at iana.org defines the namespace for warn codes.

Examples

Warning: 110 anderson/1.3.37 "Response is stale"

Date: Wed, 21 Oct 2015 07:28:00 GMT 
Warning: 112 - "cache down" "Wed, 21 Oct 2015 07:28:00 GMT"

Specifications

Browser compatibility

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• Date
• HTTP response status codes