Flash includes a separate debugger for ActionScript 3.0 that operates somewhat differently from the ActionScript 2.0 debugger. The ActionScript 3.0 debugger only works with ActionScript 3.0 FLA and AS files. FLA files must have publish settings set to Flash Player 9. When you initiate an ActionScript 3.0 debugging session, Flash launches the stand-alone debug version of Flash Player to play the SWF file. The debug Flash player plays the SWF in a separate window from the Flash authoring application window.

The ActionScript 3.0 debugger converts the Flash workspace to a debug workspace that displays panels that are used for debugging, including the Actions panel and/or Script window, the Debug console, and the Variables panel. The Debug console displays the call stack and contains tools for stepping through scripts. The Variables panel displays the variables in the current scope with their values and allows you to update those values yourself.