The key of D♭ major
D♭ E♭ F G♭ A♭ B♭ C
5 flats: B♭ E♭ A♭ D♭ G♭. Relative minor: The key of B♭ minor.
The triads of the key
I
D♭ | ii
E♭m | iii
Fm | IV
G♭ | V
A♭ | vi
B♭m | vii°
C° |
The seventh chords
Imaj7
D♭maj7 | ii7
E♭m7 | iii7
Fm7 | IVmaj7
G♭maj7 | V7
A♭7 | vi7
B♭m7 | viiø7
Cm7♭5 |
D♭ major scale
Open it in the app: 6. Harmony, in D♭