The Wayback Machine, from the Internet Archive, is a digital archive of the Internet. Users can see archived versions of web pages. The Wayback Machine supports multiple APIs enabling retrieval information about data captured by Wayback.
The Wayback Availability JSON API provides a test to see if a particular url is archived and accessible from the Wayback Machine. The API can check to see if an archived copy is ready to display by providing a 404 or other error handler.