This is my user agent
Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.64 Safari/537.31
I know I am
From developer.mozilla.org:
User-Agent: <product> / <product-version> <comment> Common format for web browsers: User-Agent: Mozilla/<version> (<system-information>) <platform> (<platform-details>) <extensions>
<product> A product identifier <product-version> A version number of the product. <comment> Zero or more comments containing sub product information, for example.
Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:47.0) Gecko/20100101 Firefox/47.0
Mozilla/5.0 (Macintosh; Intel Mac OS X x.y; rv:42.0) Gecko/20100101 Firefox/42.0
The Chrome (or Chromium/blink-based engines) user agent string is similar to the Firefox format. For compatibility, it adds strings like "KHTML, like Gecko" and "Safari".
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36
Mozilla/5.0 (iPhone; CPU iPhone OS 10_3_1 like Mac OS X) AppleWebKit/603.1.30 (KHTML, like Gecko) Version/10.0 Mobile/14E304 Safari/602.1
Mozilla/5.0 (compatible; MSIE 9.0; Windows Phone OS 7.5; Trident/5.0; IEMobile/9.0)
User Agent string provide information on application type, operating system, software vendor / version and layout rendering engine.
Depending on browser you would also get additional information. IE provides Feature Tokens that contains information about .NET runtime versions. You can learn more about IE specific tokens here - http://msdn.microsoft.com/en-us/library/ms537503(v=vs.85).aspx
Not sure if you would need this but will surely help to understand how user agent strings are decoded - http://www.texsoft.it/index.php?c=software&m=sw.php.useragent&l=it