Observed arrival · 2026-09-22
Key Formula, a Playable Chord Lab
An interactive piano tool teaches chord construction through interval math, keyboard practice, drills, MIDI input, and sampled instruments.
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$Paid
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✦Pretty
●Pro
◎Niche
◉Human
⚑Risk
ƒJS
- For
- Piano learners studying chord construction
- Worth noticing
- Chord formulas are shown as semitone steps, with selectable voicings from root position through second inversion.
Field notes
The interface makes interval arithmetic visible alongside the keyboard: the example C Major 7th is rendered as successive +4, +3, and +4 semitone moves. Users can switch among grand piano, electric, and organ sounds, adjust volume, sustain, and release, and connect MIDI hardware. The page also exposes drill and progress sections, while the mood-based progression maker is presented as an AI feature rather than independently verified functionality.
Observed signals
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Editorial observations of this landing page, not a rating.
○OpenPublic substance visible
✦PrettyNotable craft visible
●ProPolished or operationally mature
◎NicheUnusually specific use
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