Why This App
Music theory is worth learning. It explains why some combinations of notes feel settled and others feel restless, and it gives you a vocabulary for talking about that. But a lot of what gets taught alongside it isn't really about how music works - it's about how music got written down, or how it happens to sit on a particular instrument. Those are different things, and conflating them is where a lot of the confusion comes from. A student can spend an hour arguing about whether a note is A-sharp or B-flat and come away having learned nothing about how the chord actually sounds.
This app is opinionated about which is which. It keeps the parts of theory that describe harmony itself, and it deliberately drops the parts that exist for notational or historical reasons - the ones that tend to confuse a learner or start a pointless argument about naming, without changing anything about what you'd hear.
What actually matters
The harmony itself - which notes are sounding together, and what that combination feels like. Everything else on this page is in service of this one thing.
Intervals and chord quality- a small, useful vocabulary for what you're hearing. “Minor third,” “major triad,” “dominant seventh” are worth knowing because they name something about the sound, not about the page.
Scale names - Dorian, harmonic minor, and the rest are shorthand for specific, recognizable patterns of steps. Worth learning the pattern; see Scales for how they relate to each other.
Chord progressions and harmony over time - how one chord moves to the next, and how that motion repeats and develops, regardless of which key it happens to be transposed into. A ii-V-I is the same shape whether it starts on C or on F-sharp.
What we leave out
Chord spelling.Whether a note is written as G-sharp or A-flat matters to someone reading sheet music in a particular key, and not at all to your ear. You will never see a double sharp or a double flat in this app, even on the rare chord where that's the “correct” spelling - the wheel just shows the note.
Whole-whole-half-whole-whole-whole-half.The step recipe is a real pattern, but memorizing a string of letters is a workaround for not being able to see the pattern directly. Once you can see it, you don't need to recite it.
What key you're in.Key signatures tell you how a piece is notated, not how it sounds. The wheel doesn't care what key a chord or scale is in - transposing just rotates the same shape to a different starting point.
Where it sits on an instrument.We show a piano for reference, because it's a familiar layout and a convenient way to play a sound back. But the specific arrangement of black and white keys is an accident of one particular instrument's design - it doesn't explain the harmony, and it can make an otherwise simple relationship look irregular for no musical reason. Understanding a chord doesn't require a piano, or a guitar, or any instrument at all.
Why the wheel
The chromatic circle is a cleaner way to look at harmony than a keyboard or a staff, because it's built around one idea: distance. Notes are arranged by how far apart they are, not by which letter they're named after or where they happen to fall on a particular instrument. Transposing a chord to a new key doesn't reshape it or relabel half its notes - it just spins the same shape to a new position.
That's also why the wheel is colored the way it is: things that sound similar, look similar. Every wedge and every chord blend is derived from interval distance rather than note names, so a relationship you can hear shows up as a relationship you can see - see Color Coding for how that works.