In IE, the eighth version of the built-in tools developer and has undergone dramatic changes in the moment of its functionality can be compared with plugin'om FireBug for the browser Firefox. So the process of developing and debugging solutions for dynamic sites with IE8 tool turns into a holiday that is evident from the previous "Achievements IE. The eighth version of IE should be emphasized: a multifunctional web developer tools; intelligible description of the error script'ov; integrated DOM - Inspector, the ability to track the status of requests. Despite the universal distribution to ordinary Internet users, from professional web developers IE5-IE7 has a bad name. As for the developer tools built into IE8 yet they are difficult to adequate assessment and as a community of professional web developers react to this innovation Microsoft is hard to say. On the other hand it is likely that if Microsoft did not throw attempts to implement really worthwhile product aimed not only to view the contents of Web pages, but also on website development, it is quite possible that after a while IE will be able to move even a spike as FireBug. Firefox console console debugging of Firefox, in the form in which it exists today, is seen one of the best built-in testing tools, which noted the quality of community JavScript programmers. Among the many benefits of the console Firefox, it should be emphasized especially the following: The ability to enter arbitrary JavScript commands, which helps to easily determine the current values, which are the variables after loading stranitsy.Konsol allows you to sort messages by type (for example: errors, warnings, etc.). Ability to get information not only about errors in JavScript code, but additional warnings associated with errors and critical discrepancies in style sheets. Moreover, significant advantage is the availability of Firefox extensions DOM - Inspector, that application which lets you view the current (after or during the script'a) status HTML tree.