What’s a Browser User-Agent String?


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A Browser User-Agent is information that your browser passes along to websites when you visit any particular web page. It’s benign information – mostly about the browser itself to help optimize your experience. There are tons of different web browsers available to use, and each of them has their own unique user-agent string.

When you visit a Web page, your browser sends the user-agent string to the server hosting the site that you are visiting. This string indicates which browser you are using, its version number, and details about your system, such as operating system and version. The Web server can use this information to provide content that is tailored for your specific browser.

The easiest way for you to analyze your own user-agent string is to visit the UserAgentString web site. As soon as you go to the site, you’ll see that your information is displayed on the page, such as the browser and operating system you are using. You can also analyze it on the page – learning what each part means.

This information is being passed along, whether you knew it or not. Other information is being passed along, as well – such as whether javascript is turned on. None of these things are something that should be hidden, or covered up. It’s a good thing for developers to be able to see this information, so that they can make sure their site is working properly for your particular browser.

Trying out this site won’t help you figure out what browser may be the fastest, but it will give you information about the browsers that you may not have known.

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5 thoughts on “What’s a Browser User-Agent String?”

  1. UserAgentString.com thinks that Safari 4 is a Mozzila based browser, and it also says “like Gecko” whatever that means.

  2. “None of these things are something that should be hidden, or covered up.” – Hmmm, I’d have to disagree there, true if the site visited is Mostly Harmless, but a malicious site will tailor its exploits to the browsers’ vulnerabilities – there’s also a server agent string that comes back, think unpatched IIS for what a scriptkiddie could do with that info.

    A number of web cache / load balancing devices rewrite the UAS to help get around this (think of the ISP hosting colo sites, where customer servers may be running any server on any platform), forcing strict HTTP and returning a null or garbage (or even the name of the appliance vendor’s kit, hopefully they won’t have exploits for security devices…) for the server agent – helpful in an environment where security counts!

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