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 navigator.userAgent property.
A typical user agent string looks like this: "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:124.0) Gecko/20100101 Firefox/124.0".
See also
- User agent on Wikipedia
navigator.userAgent- Browser detection using the user agent
- RFC 2616, section 14.43: The
User-Agentheader - Browser (glossary)
- HTTP Headers