Web - User Agent (UA)


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

The most well-known user agent is a web browser but it can also be a bot

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


The user agent string is a a string that represents the identifier of a user-agent.

It's send by the browsers with the User-Agent HTTP headers.

Documentation / Reference

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