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Updated:03:40 PM CT Jan 01, 2007
Posted:01:14 PM CT Jan 01, 2007

What is a User Agent?

Author: Steve Lautenschlager

BrowsersClient SideWeb

 Summary

A User Agent is a string that a web browser passes to a web server or website telling it what type of browser it is and what type of platform it's running on. It is not a reliable indicator since many browsers try to spoof others so that they won't be locked out from websites that try to require a certain type of browser.

Click here to see what your browser is saying about itself.

 What is a User Agent?

For a great list of sample web browsers and user agent strings visit Zytrax.com.

When you visit a website your browser displays a certain amount of information to the website. Sometimes this information is used to help the website customize the experience for you.

Some of the information exposed by the user agent is what type of browser you are using, your operating system version and perhaps if you have certain software applications installed.

Because some websites are customized for certain browsers while blocking others, most browsers started displaying information in the user agent to trick sites into thinking they are the required browser. Bad idea.

For example, theoretically only Internet Explorer should contain the string MSIE to tell a website this is Internet Explorer. But other browsers started adding this string to their user agent to fool websites. This practice would be fine if all browsers supported all features in the same way, but they don't. This usually means that browsers entering websites where they were not designed to tread will break or fail to properly view the site.

This web page allows you to see the user agent string your browser is displaying to the world.

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Steve Lautenschlager (steve)
Steve is the founder and creator of Cambia Research. Developing and maintaining the site combines his passions for technology, writing and education.
Steve holds a Ph.D. in particle physics from Duke University, has worked at CERN, the European center for particle physics (where the web was born) and in Microsoft's web division with microsoft.com, msnbc.com and other web properties. Steve is a web consultant specializing in Microsoft.NET technologies. Read more here.


 
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