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.

The Memento served at the end of the negotiation carries a Memento-Datetime response header indicating the exact capture date of the snapshot. That header travels on the 200 OK Memento response alone. A TimeGate answering with 302 Found sends the Location and a Link header naming the original resource, and the specification forbids Memento-Datetime on the redirect itself.

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

The server responds with a redirect pointing at the closest available Memento.

HTTP/1.1 302 Found
Location: /web/20200702/https://example.re/
Link: <https://example.re/>; rel="original"
Vary: Accept-Datetime

Following the redirect returns the Memento itself with 200 OK and the Memento-Datetime header naming the capture date.

See also

Last updated: September 21, 2026