To check the variables of the script contained in an AppleScript terminal or in a script window, press ⌥⌘R.

Then a summary window opens containing the following information about the script defined in the window:

• if some undefined variables are found, they are listed. This is probably some bugs that you want to fix.
• if some unused variables are found, they are listed. This may be not an error, but this information may be relevant nevertheless.