Script Debugger displays the names and values of persistent variables (top-level entities — script objects, script properties, and globals) contained in your script. They are shown in the result drawer, in the third pane, whose columns are headed “Variable” and “Value”. This is the variables pane.

For example, running this script:

property x : missing value
set x to "Hello there!"

results in the variables pane looking like this:

The notion “contained in” is made more complicated by AppleScript’s script object inheritance mechanism. By default, your script’s parent is the AppleScript scripting component, so your script effectively “contains” the top-level entities of this virtual script object — and Script Debugger displays it. In the above illustration it displays it twice, once by virtue of being the script’s parent, and again by virtue of being the named virtual script object AppleScript, which is always globally accessible.

The variables pane is an explorer view, with all that this entails. For example, you can double-click a line of the variables pane to see that value displayed in its own viewer window. You can also edit (change) the value of persistent top-level entities shown in the variables pane (for example, in the above illustration, the property x is editable); you might use this feature to experiment with your script’s behavior under different initial values of your persistent entities. (Script Debugger preserves the value of persistent top-level entities when a script is saved and re-opened.)

The variables pane has a more extended role during debugging. It then displays not only persistent top-level entities, and not only after the script has run — it displays all variables, while the script is still in the process of running.