User Agent

Sometimes abbreviated as UA, the user agent is a browser text string that is given to each website you visit. The user agent text string contains information such as the browser version, compatibility, operating system and version and any plugins that modify the user agent. Using this information a website can know what the capabilities of your computer are to help display the page properly.

Click here to view your UA

Below are some examples of user agents and some additional information about each of these text strings.

Mozilla/4.0 is still used for historical reasons as stated by Microsoft and is not to be confused with the variants of Mozilla browsers such as Firefox. Next, is the actual Microsoft Internet Explorer version: "compatible; MSIE 6.0;" which indicates this user has Internet Explorer 6.0. Next, "Windows NT 5.1; SV1;" is a description of the operating system in this case this user agent is using Microsoft Windows XP with Service Pack 1. Finally, the .NET CLR 1.1.4322 is the .NET framework. Often the user agent strings with Internet explorer will have various .NET versions.

In this second example this user agent is on a Linux variant. The first thing noticeably different about this user agent is the X11; which is variant of X Windows, next U; is the encryption level, which is short for USA and an indication of strong encryption. In the past different browser encryption versions had to be released for different parts of the world because of laws in the United States. Other encryption types were I; and N; although today all browsers in all parts of the world use U;. Next, i686; and Fedora/2.0.0.13-1.fc8 is the platform and type of OS. Next, en-US; is the language and location of the browser, in this case English and US. Finally, Firefox/2.0.0.13 is the browser type and version.

In this last example this user agent is a Apple Macintosh computer. As can be seen it has a lot of similarities as the above example, which is also running Firefox. However, this user agent does list Macintosh as the type of computer and Intel Mac OS X 10.5; which is the processor type and operating system. Apple computers that are not running an Intel processor will be displayed as PPC.

Different Windows versions in the user agent

Below is additional information about each of the different versions of Microsoft Windows and their corresponding user agent string codes.

Windows 95 = Windows 95 or Win95
Windows 98 & 98 SE = Windows 98 or Win98
Windows CE = Windows CE
Windows ME = Windows 9x 4.90
Windows NT 4.0 = Windows NT 4.0
Windows 2000 = Windows NT 5.0
Windows XP = Windows NT 5.1
Windows Server 2003 / XP x64 edition = Windows NT 5.2
Windows Vista = Windows NT 6.0

How to get this information

There are various ways to get this information to be displayed or gathered if you're a developer of a website. As shown in the example at the beginning of the page using JavaScript is an easy way to display the user agent to the visitor. However, if you're wanting to gather the information or manipulate it may be better to use a server side scripting language such as Perl to gather the information. Below is an example of how to display the user agent in Perl.

• See our System Information script for an example of a script taking full advantage of the user agent information and other information obtainable through JavaScript.

Also see: Browser