WebFinger

WebFinger is a protocol specified by the Internet Engineering Task Force IETF in RFC 7033 that allows for discovery of information about people and things identified by a URI. Information about a person might be discovered via an  URI, for example, which is a URI that looks like an email address.

WebFinger is specified as the discovery protocol for OpenID Connect, which is a protocol that allows one to more easily log in to various sites on the Internet.

The WebFinger protocol is used by federated software, such as GNU social, Diaspora, or Mastodon, to discover users on federated nodes and pods, as well as the remoteStorage protocol.

As a historical note, the name "WebFinger" is derived from the old ARPANET Finger protocol, but it is a very different protocol designed for HTTP.

The protocol payload is represented in JSON format.

Basic example with profile page and business card
Client request:

Server response:

Usage on Mastodon
On Mastodon, any federated servers can look up users by sending a request to the WebFinger endpoint on other servers. Here is an example for the user :

Client request: Server response: