Pick any key and mode and see every chord that fits, then drop them into a sequencer and hear the progression

Choose a root and one of 70+ scales and modes to see the scale on a piano or guitar and its triads, sevenths and extensions. A scratchpad sequencer and a MIDI practice mode let you test progressions and train chord recognition.

Notes

Creator attribution rests on Bjørn Wikkeling's own blog write-up of the tool (HN author handle is magikMaker); the tool's own pages don't name him. Maker doesn't state AI use.