If-Modified-Since

Only send the body if it changed after this date.

Request header (sent by clients) conditional

How it works

Returns 304 when unchanged. ETags are more precise.

Example

If-Modified-Since: Sat, 18 Oct 2026 09:00:00 GMT

See it live: send any request in Endpoint Client and open the Headers tab, where every response header is explained. Specification: RFC 9110.

Related headers

ETag

An identifier for this exact version of the resource.

If-Match

Only perform the change if the resource still has this ETag.

If-None-Match

Only send the body if the ETag differs.

Last-Modified

When the resource last changed.