Memento is a United States National Digital Information Infrastructure and Preservation Program (NDIIPP)–funded project aimed at making Web-archived content more readily discoverable and accessible to the public.
Memento is defined in RFC 7089[1] as an implementation of the time dimension of content negotiation.
[2] HTTP accomplishes negotiation of content via a variety of headers that allow clients and servers to find content that the user desires.
The Last-Modified header provided by HTTP[4] does not necessarily reflect when a particular version of a web page came into existence.
[5] Copies of page can be found by simply navigating, in a web browser, to a link formatted, replacing urltoarchive with the full URL of the page desired:[6] JSON description of a Memento: redirect to a Memento with a datetime that is close to a desired datetime: