On the Web, a user agent is a

software agent In computer science, a software agent is a computer program that acts for a user or another program in a relationship of agency. The term ''agent'' is derived from the Latin ''agere'' (to do): an agreement to act on one's behalf. Such "action on ...

responsible for retrieving and facilitating

end-user In product development, an end user (sometimes end-user) is a person who ultimately uses or is intended to ultimately use a product. The end user stands in contrast to users who support or maintain the product, such as sysops, system administrato ...

interaction with Web content. This includes all

web browser A web browser, often shortened to browser, is an application for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's scr ...

s, such as

Google Chrome Google Chrome is a web browser developed by Google. It was first released in 2008 for Microsoft Windows, built with free software components from Apple WebKit and Mozilla Firefox. Versions were later released for Linux, macOS, iOS, iPadOS, an ...

and

Safari A safari (; originally ) is an overland journey to observe wildlife, wild animals, especially in East Africa. The so-called big five game, "Big Five" game animals of Africa – lion, African leopard, leopard, rhinoceros, African elephant, elep ...

, some

email client An email client, email reader or, more formally, message user agent (MUA) or mail user agent is a computer program used to access and manage a user's email. A web application which provides message management, composition, and reception functio ...

s, standalone

download manager A download manager is a type of software that manages the downloading of files from the Internet, which may be built into a web browser, or as a standalone program. Functions A download manager manages files being downloaded from the internet. ...

s like youtube-dl, and other command-line utilities like cURL. The user agent is the client in a client–server system. The

HTTP HTTP (Hypertext Transfer Protocol) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, wher ...

User-Agent header is intended to clearly identify the agent to the server. However, this header can be omitted or spoofed, so some websites use other detection methods.

References

Clients (computing) {{Web-stub