Last-Modified

When the resource last changed.

Response header (sent by servers) conditional

How it works

Clients send it back in If-Modified-Since.

Example

Last-Modified: Fri, 17 Oct 2026 12:30:00 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-Modified-Since

Only send the body if it changed after this date.

If-None-Match

Only send the body if the ETag differs.