Assembly: System.Web (in system.web.dll)
You can use this class to append messages to specific trace categories. For example, if you are creating an instance of the Calendar class for your application, you might include the trace message "Starting To Render" in a rendering procedure, and "Raising OnChange Event" in an event handler procedure.
You can also use the TraceContext class to obtain a set of trace records at the end of request execution for custom processing. For more information, see ASP.NET Tracing.
To enable tracing, set the Trace attribute in the @ Page directive or the IsEnabled property to true. When tracing is enabled, in addition to showing user-provided trace content, the Page class automatically includes performance data, control-tree structure information, and state management content for every request.
|Walkthrough: Using Tracing in Visual Web Developer to Help Find Web Page Errors||Building ASP .NET Web Applications in Visual Studio|