Same notes, different order. Pick the one whose bass note leads best from the chord before it — which is what the next panel does for you.
Every chord is chosen from its own inversions to sit as close as possible to the one before it. Nothing about which chords they are changes — only which of the same notes you put where.
Worked out by trying every note in turn as the root and matching what is left against the interval patterns. If the lowest note is not the root, it says so with a slash — C/E is a C chord with an E underneath.
The chord itself is easy: a major triad is 0, 4, 7 semitones from its root, and every chord on this page is a list like that added to a note number. What takes the work is everything after — which order to put those notes in, which hand plays what, which finger goes where, and which of the several correct answers is the one that follows best from the chord you just played.
The black keys on a piano are not centred between the white ones, and a diagram that spaces them evenly looks wrong to anyone who plays. The real constraint is that the visible front of every white key is the same width — otherwise the gaps your fingers use would be uneven — and that single rule places all five black keys.
In the group of three white keys, three equal fronts share what is left after two black keys are removed; in the group of four, four fronts share what is left after three. Run that and C♯ sits noticeably nearer C, D♯ nearer E, G♯ almost exactly on the boundary between G and A, and A♯ nearer B — which is what a piano actually looks like, and why you can find your way around one in the dark.
Building C major from "C major" is a lookup. Going the other way — you press four keys, what is that? — means trying each note in turn as the root, measuring the others against it, and seeing which arrangement matches a pattern. Most sets match nothing; a few match more than one, and then the tie is broken by which note is in the bass. Where the bass is not the root, the answer is a slash chord, because that is genuinely what it is: the same chord, standing on a different foot.
Play C, then F, then G, then C, all in root position, and your hand jumps around the keyboard and the result sounds like four separate events. Choose a different inversion of each and the same four chords can be played with the notes barely moving — most of them staying exactly where they are.
That is a small search rather than a matter of taste: for each chord, try every inversion in every reachable octave, and keep the one whose notes are closest to the chord before it. The page reports the total distance travelled both ways, and the smoothed version is typically less than a third of the root-position one. It is the single biggest difference between a chord chart and something that sounds like piano playing.
Not its name and not its function, but it changes what the bass is doing, and the bass is most of what a listener hears as movement. C major with an E at the bottom is still C major; it just feels like it is on its way somewhere rather than sitting still. That is why the choice matters even though the notes are identical.
Because the right fingering depends on what comes next, and this page does not know. The numbers shown are the conventional ones for each shape played on its own — thumb on the lowest note in the right hand, little finger on the lowest in the left — and they are a sound default. Inside a real passage, a fingering that sets up the following chord beats a fingering that is comfortable in isolation.
Because that is usually what sounds best. Three or four notes stacked in the bottom octave turn to mud: the lower the notes, the more the overtones of one interfere with the fundamental of another. Root and fifth, or just the root, leaves the harmony to the right hand where it stays legible. The tool follows that convention and lets you override it.
A chord with a specified bass note that is not its root — written C/E and said "C over E". Most of the time it is simply an inversion given a name, because the bass player or the left hand needs telling which note to take. Occasionally the bass note is not in the chord at all, which is a different and more interesting thing.
The theory is identical and the shapes are not, because a guitar cannot play any six notes you like. Guitar chords works the same problem out against six strings and a hand that can reach four frets.
Twelve-tone equal temperament and a standard 88-key layout. The keyboard proportions come from the equal-front construction described above with a black key about 0.58 of a white key's width, which is close to most modern pianos but not identical to any particular maker. Fingerings are conventional defaults for isolated chords. The voice-leading search minimises total semitone movement, which is one reasonable definition of smooth and not the only one — real voice leading also avoids parallel fifths and keeps the melody on top, and neither of those is modelled here.
No change to this page at all since the earliest archived release (v4.72). The full history for the site is in the changelog.