For Windows users, HARMONY also has the ability to check the song's mode against its key signature.

When you generate chords, it will ask if it thinks the mode is wrong, and suggest what it could be.

For safety, HARMONY will not generate 'dominant 7th' chords if the tune is known to be modal, because these are not applicable to all modes. (For example, just play G instead of G7 before a C)

(Actually, that is one way of checking from printed music - lack of 7ths can indicate modes, particularly Dorian & Aeolian)