WebFinger (RFC 7033) is a REST-based web service used to discover information about people and other addressable entities on the Internet.
WebFinger servers return a JSON document as a response to a valid query. The JSON document is referred to as a JSON Resource Descriptor (JRD) document. The structure of the document is simple, providing the querying client with a list of link relations, properties, and other information about the subject being queried.
End users publish information about themselves through an account, such as a social network account or a corporate directory. The service provider or enterprise maintaining the account would then publish the information about the user marked for publication via WebFinger. It is then possible for other users to retrieve that information from within the applications they use. As an example, a user might publish his name, address, phone number, and picture via WebFinger. This information could then appear automatically in an email client used by another user.
WebFinger may be used for discovering other kinds of information about a host or domain. It is certainly not limited to discovering information about human users. For example, it could be used to discover the information required to properly configure an email client or to determine the physical location of a printer or other device on the network.