C#

In the newest version?

You cannot directly debug inside the Studio. You can use the Run button to test your script execution. You can use the message.DebugPrint("message") command to output values to the script editor.

You can also develop scripts via Visual Studio itself and then paste the script into the studio.

See:
https://ta5.blob.core.windows.net/ta5help/ThinkAutomation.html#using-visual-studio-to-develop-custom-action-code