On the Web, a user agent is a software agent responsible for retrieving and facilitating end-user interaction with Web content.
[1] This includes all web browsers, such as Google Chrome and Safari, some email clients, standalone download managers like youtube-dl, and other command-line utilities like cURL.
The HTTP User-Agent header is intended to clearly identify the agent to the server.
[2] However, this header can be omitted or spoofed,[2] so some websites use other detection methods.
This World Wide Web–related article is a stub.