This response header contains the time when the content in the response body was last modified.
Last modification times can be used to prevent unnecessary re-rendering of unchanged content.
See Conditional requests for details and examples.
The header value is a date/time in RFC 1123 format:
Last-Modified: Wed, 15 Nov 2000 13:11:22 GMT
For a readable description of the time format, see MDN.
Alternatives
Instead of sending this header, the server may also render fragments with [up-time] attributes.
