Name
Vary
Synopsis
The Vary header is used by servers to inform clients what headers from a client’s request will be used in server-side negotiation.[10] Its value is a list of headers that the server looks at to determine what to send the client as a response.
An example of this would be a server that sends special HTML pages based on your web browser’s features. A server sending these special pages for a URL would include a Vary header that indicated that it looked at the User-Agent header of the request to determine what to send as a response.
The Vary header also is used by caching proxies; see Chapter 7 for more on how the Vary header relates to cached HTTP responses.
Type
Response header
Basic Syntax
Vary: (“*” | 1# field-name)
Example
Vary: User-Agent
[10] See Chapter 17 for more on content negotiation.
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