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.

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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.

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To understand Memento fully, one must realize that the Last-Modified header provided by HTTP^[4] does not necessarily reflect when a particular version of a web page came into existence. Also, the Last-Modified header may not exist in some cases. To provide more information, the Memento-Datetime header has been introduced to indicate when a specific representation of a web page was observed on the web.^[5]

One can find copies of page 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:

http://timetravel.mementoweb.org/api/json/YYYY/urltoarchive

http://timetravel.mementoweb.org/api/json/YYYYMM/urltoarchive

http://timetravel.mementoweb.org/api/json/YYYYMMDD/urltoarchive

http://timetravel.mementoweb.org/api/json/YYYYMMDDHH/urltoarchive

http://timetravel.mementoweb.org/api/json/YYYYMMDDHHMM/urltoarchive

or

redirect to a Memento with a datetime that is close to a desired datetime:

http://timetravel.mementoweb.org/memento/YYYY/urltoarchive

http://timetravel.mementoweb.org/memento/YYYYMM/urltoarchive

http://timetravel.mementoweb.org/memento/YYYYMMDD/urltoarchive

http://timetravel.mementoweb.org/memento/YYYYMMDDHH/urltoarchive

http://timetravel.mementoweb.org/memento/YYYYMMDDHHMM/urltoarchive