An interactive computer program that provides a user interface to a client-server or peer-to-peer application. Modern user agents often provide a friendly, easy to use, graphical user interface that hides the details of the underlying application protocol. In many cases, a user agent will implement the client-side protocols of a networked application, creating and destroying sockets for network communications, sending the client-side messages of the application protocol on behalf of the user, and parsing and displaying the server responses.

Examples of well known user agents are web browsers, e-mail clients, instant messaging clients, FTP clients, telnet clients, file sharing tools, etc. Depending on the application, a single user agent may be able to provide an interface to more than one application protocol. For example, a web browser can typically provide access to Telnet, HTTP, FTP and others, and an email client will typically be able to “speak” SMTP, POP and IMAP (in addition to HTTP for access to webmail mailboxes).

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