User agent
A user agent is a computer program representing a person, for example, a browser in a Web context.
Besides a browser, a user agent could be a bot scraping webpages, a download manager, or another app accessing the Web. Along with each request they make to the server, browsers include a self-identifying User-Agent HTTP header called a user agent (UA) string. This string often identifies the browser, its version number, and its host operating system.
Spam bots, download managers, and some browsers often send a fake UA string to announce themselves as a different client. This is known as user agent spoofing.
The user agent string can be accessed with JavaScript on the client side using the NavigatorID.userAgent property.
A typical user agent string looks like this: "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0".
See also
- User agent on Wikipedia
NavigatorID.userAgent- Browser detection using the user agent
- RFC 2616, section 14.43: The
User-Agentheader - Glossary:
- HTTP Headers