key signature
G♭ major
G♭1A♭2B♭3C♭4D♭5E♭6F7
6 flats, written B♭ E♭ A♭ D♭ G♭ C♭
The chords that live in it
G♭degree 1 · majorA♭mdegree 2 · minorB♭mdegree 3 · minorC♭degree 4 · majorD♭degree 5 · majorE♭mdegree 6 · minorFdimdegree 7 · diminished
Built by stacking thirds inside the scale and asking what quality comes out, rather than from a table of roman numerals.
What is true of it
G♭ major has 6 flats.
They are written in this order, always: B♭ E♭ A♭ D♭ G♭ C♭.
Its notes are G♭, A♭, B♭, C♭, D♭, E♭ and F.
Relative: E♭ minor has the same 6 flats. Parallel: G♭ minor has 9 flats, which is why changing mode changes the signature by three.
Every key
C♭ majorD♭ majorA♭ majorE♭ majorB♭ majorF majorC majorG majorD majorA majorE majorB majorF♯ majorC♯ majorA♭ minorE♭ minorB♭ minorF minorC minorG minorD minorA minorE minorB minorF♯ minorC♯ minorG♯ minorD♯ minorA♯ minor