Microsoft Script Debugger is relatively minimal debugger for Windows Script Host-supported scripting languages, such as VBScript and JScript. Its user interface allows the user to set breakpoints and/or step through execution of script code line by line, and examine values of variables and properties after any step. In effect, it provides a way for developers to see script code behavior as it runs, thus eliminating much of the guess-work when things do not quite work as intended.
Microsoft considers it to be deprecated. Also, Internet Explorer 8 comes with a different, tightly integrated JScript debugger part of the Internet Explorer Developer Tools.[1]