Selenium is completely free test automation tool, while Silk Test is not. Only web applications can be analyzed using Selenium testing suite. However, Silk Test can be utilized for testing client-server programs. Selenium supports following browsers: Internet Explorer, Firefox, Safari, Opera or Konqueror on Windows, Mac OS X, and Linux. Yet, Silk Test is limited to Ie and Firefox. Silk Check uses 4Test scripting language. Yet, Selenium test-suite has the flexibility to use many languages like Java,.Net, Perl, PHP, Python, and Ruby.