can be used with GET or HEAD to make the method conditional by modification date: if the selected representation has not been modified since the time specified in this field, then do not perform the request method; instead, respond as detailed below.
Quick facts
Description
can be used with GET or HEAD to make the method conditional by modification date: if the selected representation has not been modified since the time specified in this field, then do not perform the request method; instead, respond as detailed below.
Syntax
If-Modified-Since: Mon, 17 Aug 2026 10:00:00 GMT
Related status codes
Frequently asked questions
can be used with GET or HEAD to make the method conditional by modification date: if the selected representation has not been modified since the time specified in this field, then do not perform the request method; instead, respond as detailed below.
It is classified as a request header and can appear in requests or responses depending on context.
Sources & standards
Updated 2026-09-13
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