User Agent String Analyzer

Please enter user agent string


About User Agent String Analyzer

A user agent is a client application implementing a network protocol used in communications within a client-server distributed computing system. The term most notably refers to applications that access the World Wide Web, but other systems, such as the Session Initiation Protocol (SIP), use the term user agent to refer to both end points of a communications session.

Web user agents range from Web browsers to search engine crawlers (spiders), as well as mobile phones, screen readers and braille browsers used by people with disabilities. When a user agent operates, it typically identifies itself, its application type, operating system, software vendor, or software revision, by submitting a characteristic identification string to its operating peer. In the HTTP and SIP protocols, this is transmitted in a header field User-Agent. Bots, such as Web crawlers, often also include a URL and/or e-mail address so that the Webmaster can contact the operator of the bot.

Some user agents identify their software as part of the client-server conversation. In HTTP and SIP, the identity is transmitted via the User-Agent request header, as described by RFC 1945. This string is then used by the communications partner to characterize the client and optionally select suitable content or operating parameters for session. For example, this may be used to provide properly formatted content for desktop computers and for smartphones.

The user agent string is one of the criteria by which Web crawlers may be excluded from accessing certain parts of a Web site using the Robots Exclusion Standard (robots.txt file).


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