User agent#User agent spoofing

{{Short description|Software acting on behalf of a user}}

{{Distinguish|User-Agent header}}

On the Web, a user agent is a software agent responsible for retrieving and facilitating end-user interaction with Web content.{{cite web|url=https://www.w3.org/WAI/UA/work/wiki/Definition_of_User_Agent |title=W3C Definition of User Agent |publisher=www.w3.org |date=2011-06-16 |access-date=2018-10-20}} 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.{{cite web |title=User agent |url=https://developer.mozilla.org/en-US/docs/Glossary/User_agent |website=MDN Web Docs|date=8 July 2024 }}

The user agent is the client in a client–server system. The HTTP 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.