MusicReasonScales, Keys, Intervals, and Notation
What does this key signature mean?
Choose a major or minor tonic and see its signature accidentals, one-octave scale, and relative key, without treating the signature alone as proof of a song's actual key.
Answer
Want to learn more? Keys, Modulation, and Harmonic Direction
Understand
"Relative" keys share one key signature; "parallel" keys share one tonic. C major and A minor are relative (same signature, no sharps or flats); C major and C minor are parallel (same tonic, different signatures). A key signature by itself cannot tell you whether a piece is actually in the major key or its relative minor, and it makes no claim about automatic harmonic function: that reading requires looking at the actual chords and cadences used, not the signature alone.
Worked example
E-flat major uses three flats, applied in a fixed order: B-flat, E-flat, and A-flat. Its one-octave scale is E-flat, F, G, A-flat, B-flat, C, D, and back to E-flat. Its relative minor, sharing that same three-flat signature, is C minor.
Method and limitations
Major signatures follow the circle-of-fifths mapping: each step of a fifth away from C adds one sharp (clockwise) or one flat (counterclockwise), applied in the traditional fixed order. Natural minor uses its own scale formula and shares its relative major's signature rather than generating a separate one. Harmonic and melodic minor are scale forms available from Scale Explorer, not alternate key-signature routes here: a key signature by definition describes only the diatonic (natural minor or major) collection. This tool covers the launch range of -7 through +7 fifths and does not manufacture a theoretical key signature beyond that range.
Why the accidental order is fixed
Sharps and flats are not added to a key signature in an arbitrary or memorized order: each new sharp or flat is the note a fifth away from the previous one in the circle of fifths, which is why F-sharp always appears before C-sharp in any sharp key, and B-flat always appears before E-flat in any flat key. That fixed order is also why you can read a signature's fifths count directly off how many accidentals it shows, without needing to look up each individual key by name.