Notes, frequencies, intervals, scales, chords, keys, transposition, tempo math and Roman numeral analysis.
payments ON MAINNET (real money) · 10 live endpoints
| Endpoint | Price | What it answers |
|---|---|---|
GET /chord-name | $0.02 | Name a chord from its notes (C E G Bb, A C E G): best name, inversion and alternative names; first note is the bass. |
GET /chord | $0.02 | Spell a chord from its symbol (Cmaj7, F#m7b5, G7b9, Dsus4, C/E): notes, intervals, semitones and MIDI numbers. |
GET /freq-note | $0.02 | Frequency in Hz to the nearest note, MIDI number and offset in cents; adjustable A4 reference; tuner-style result. |
GET /interval | $0.02 | Interval between two notes (quality, number, semitones) or the note a given interval above or below a note. |
GET /key-signature | $0.02 | Key signature (sharps or flats), circle-of-fifths neighbours, relative and parallel keys for any major or minor key. |
GET /note-freq | $0.02 | Note name (C#4, Bb3) or MIDI number to MIDI, frequency in Hz and wavelength, with adjustable A4 reference pitch. |
GET /roman-numerals | $0.02 | Roman numeral analysis of a chord progression in a key: numerals, inversions, borrowed chords, secondary dominants. |
GET /scale | $0.02 | Spell a scale or mode on any root: major, minor, modes, harmonic and melodic minor, pentatonic, blues, whole tone. |
GET /tempo | $0.02 | BPM to milliseconds for note values, dotted and triplet delay times; or average tap intervals into a steady BPM. |
GET /transpose | $0.02 | Transpose a chord progression by semitones or from one key to another, with spelling that fits the target key. |
GET /catalog returns this list as JSON. Activity hub · uptime.
Computed locally from standard Western music theory (12-tone equal temperament, scientific pitch notation with C4 as middle C and MIDI 60) and provided as is. Spelling conventions vary between sources and chord symbols are not standardised; results show the convention used. Educational and creative aid only, not a substitute for a teacher or a score. Every paid response carries a disclaimer field.