# Web - User Agent (UA)

## 1 - About

A user agent is software (a software agent) that is acting on behalf of a user.

A user agent may:

• display a document,
• read it aloud,
• cause it to be printed,
• convert it to another format, etc.

When software agent operates in a network protocol, it often identifies itself, its application type, operating system, software vendor, or software revision, by submitting a characteristic identification string to its operating peer. In HTTP, SIP, and SMTP/NNTP protocols, this identification is transmitted in a header field User-Agent