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Request

If-Modified-Since

Makes the request conditional; server responds with 304 if content hasn't changed since the given date.

Syntax

If-Modified-Since: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMT

Example

If-Modified-Since: Wed, 26 Mar 2025 07:28:00 GMT

Description

The If-Modified-Since header makes a GET or HEAD request conditional based on a timestamp. If the resource has not been modified since the given date, the server returns 304 Not Modified without a body.

It works alongside Last-Modified response header and is a simpler (but less precise) alternative to If-None-Match / ETag.

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Related Headers

Accept
Specifies the media types the client can process in the response.
Accept-Encoding
Indicates which content encodings the client can understand.
Accept-Language
Advertises the natural languages the client prefers in the response.
Authorization
Carries credentials to authenticate the client with the server.
Cookie
Sends previously stored cookies from the server back with each request.
Host
Specifies the domain name and port of the server being requested.

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