According to some embodiments, a callback interface for web accessible services is provided. A Uniform Resource Locator (URL) or similar address is issued by a host associated service to the user. User's browser provides the URL to an activity service, which on the user's behalf contacts the host service indicated by the URL and supporting the callback interface. The activity service then facilitates the user's requests on documents maintained by the host service through stateless calls to the host service providing web accessible services such as document manipulation, image processing, and similar ones.