piano scale
E♭ major
E♭1F2G3A♭4B♭5C6D7
The seven-note scale everything else is measured against: two whole steps, a half, three whole steps, a half.
The same sounds spelled from the other side are D♯ major.
Written out
Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.
The step pattern
E♭WFWGHA♭WB♭WCWDHE♭
What is true of it
E♭ major is E♭, F, G, A♭, B♭, C and D, and back to E♭.
Its steps are W – W – H – W – W – W – H, where W is a whole step and H a half.
On the same tonic, E♭ melodic minor differs from it by exactly one note.
Chords made only of these notes
CmminorCm7minor seventhDdimdiminishedDm7♭5half-diminished seventhE♭majorE♭maj7major seventhFmminorFm7minor seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.