Play a chord on a MIDI keyboard and Fretscope names it, works out the key and mode you are in, and shows you where to put your fingers. It runs in the browser and talks to your controller over Web MIDI, so there is nothing to install and nothing to authorise beyond letting the page see your keyboard.

The shape you played, not the shape it prefers

Most chord tools answer with a root-position CAGED grip regardless of what you did. Fretscope ranks guitar shapes against the voicing you actually played — its inversion, its top note and its register. Put a third in the bass and the root-position reward stands down. Play two octaves up and a shape in the wrong octave is actively penalised rather than merely not rewarded. The keyboard outranks the convention.

It will not flatter you

In strict mode an incomplete chord is reported as what it is. Play E–B♭–D and you get an E diminished fragment, not a silently upgraded rootless C9. Inferred mode will supply a missing root or perfect fifth if you want it, but it says so in the symbol — C9(no root) — rather than pretending you played the whole thing.

The simplest key that fits

Key detection counts characteristic scale tones once across everything it has heard rather than once per chord, charges a little for scale degrees it has not heard, and prefers an ordinary diatonic reading over an exotic rotation containing the same notes. Without that last rule a plain Dm7 → G7 vamp reads as B Altered — technically true, musically useless. There are 24 modes across four families in there, with Roman numeral analysis and a manual key lock for when you know better than it does.

What you need

A MIDI controller and a browser with the Web MIDI API — that means Chrome, Edge or Opera. Firefox and Safari need a flag or an extension, which is Firefox and Safari's business rather than ours.