FlexSpy is an extremely useful Flex component for developers starting to learn Flex. Similar to Firebug or the DOM Inspector in Firefox, FlexSpy allows you to dig into the visual components in your Flex application, and dynamically change properties and styles for those components in real time. This is one of those applications that is much easier to explain when you see it, so check out the demo site and click the button in the top right to launch the FlexSpy component.

The Find Component action is really cool - clicking on Find Component allows you to move your mouse over the application and see what component is being used, and what its ID is.

Intergrating FlexSpy in your Flex application is easy: add the .swc to your Flex project, then add a button to launch the FlexSpy window.

FlexSpy is an open source project hosted on Google Code.