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The HTTP Framework for Time-Based Access to Resource States, also known as the Memento framework, is a method of denoting and obtaining historical revisions of HTTP resources, such as a web pages or files accessible by URL. Development of the framework was initiated as a project of the United States National Digital Information Infrastructure and Preservation Program (NDIIPP). It was funded with the aim of making Web-archived content more easily discoverable and accessible to the public.

The Memento project announced the shutdown of its hosted TimeTravel service on 5 September 2025.^[1][2]

Memento is defined in RFC 7089^[3] as an implementation of the time dimension of content negotiation.^[4] HTTP accomplishes negotiation of content using headers that allow clients and servers to find content that the user desires.

The Last-Modified header provided by HTTP^[5] 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.^[6]

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.^[7]

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

• Memento Project
• The When of the Web - Extensive information about the proposal and experiment is available in the November 2009 paper
• Memento: Time Travel for the Web
• http://lanlsource.lanl.gov/hello
• http://www.cdlib.org/cdlinfo/2010/02/04/web-archive-discovery-memento-implementation-meeting/