Accept-Datetime

Web archives store snapshots of pages over time, and retrieving a specific snapshot requires datetime negotiation. The Accept-Datetime request header asks the server for a historical version of a resource captured at or near a specific date and time.

Table of Contents

Usage

The Accept-Datetime header is part of the Memento protocol, a framework for accessing past versions of web resources. When a client sends this header with a date value, the server looks for an archived snapshot (called a Memento) closest to the requested date.

The Memento protocol defines several roles. An original resource (the live page) is hosted on a regular server. A TimeGate is an endpoint accepting datetime negotiation and redirecting to the best-matching Memento. A TimeMap lists all available Mementos for a given resource.

After processing the request, the server includes a Memento-Datetime response header indicating the exact capture date of the returned snapshot. The response status is typically 200 OK when served directly, or 302 Found when a TimeGate redirects to the archived copy.

The date format follows the standard HTTP date syntax. Precision depends on the archive: some services store daily snapshots, others capture pages multiple times per day.

Values

HTTP-date

An IMF-fixdate timestamp specifying the preferred point in time. The format follows Day, DD Mon YYYY HH:MM:SS GMT.

Example

A client requesting a snapshot of a resource from January 2015. The date follows the required IMF-fixdate format with a GMT timezone.

Accept-Datetime: Thu, 15 Jan 2015 00:00:00 GMT

A full request to a TimeGate, asking for the version of a page archived closest to July 2020.

GET /timegate/https://example.re/ HTTP/1.1
Host: web.archive.org
Accept-Datetime: Wed, 01 Jul 2020 12:00:00 GMT

The server responds with the closest available Memento and includes the actual capture date.

HTTP/1.1 302 Found
Location: /web/20200702/https://example.re/
Memento-Datetime: Thu, 02 Jul 2020 03:14:22 GMT
Vary: Accept-Datetime

Note

The returned snapshot does not always match the exact requested date. Web archives select the closest available capture based on retention policies and crawl frequency.

See also

Last updated: April 4, 2026