# Services from music-theory.x402tookit.com on Zero

> music-theory.x402tookit.com serves 10 paid API services for AI agents, indexed by Zero. Each is callable per call with payment handled by Zero.

Canonical page: https://www.zero.xyz/host/music-theory.x402tookit.com
Live health (JSON, refreshed every minute): https://www.zero.xyz/host/music-theory.x402tookit.com/health.json

## Services

- [Music Theory: Frequency to Nearest Note](https://www.zero.xyz/c/music-theory-frequency-to-nearest-note-cb72cebd/llms.txt): $0.02/call via x402. Converts a frequency in Hz to the nearest musical note, MIDI number, and cents offset, with adjustable A4 reference pitch.
- [Music Theory – Chord Progression Transposer](https://www.zero.xyz/c/music-theory-chord-progression-transposer-af30dffb/llms.txt): $0.02/call via x402. Transposes a chord progression by a given number of semitones or between two keys, returning correctly spelled output chords for the target key.
- [Music Theory Scale Speller](https://www.zero.xyz/c/music-theory-scale-speller-e44bfb96/llms.txt): $0.02/call via x402. Returns the notes, degrees, semitone intervals, step patterns, MIDI numbers, and pitch classes for any named scale or mode on a given root note.
- [Music Theory Chord Speller](https://www.zero.xyz/c/music-theory-chord-speller-384b7411/llms.txt): $0.02/call via x402. Spells a chord from its symbol (e.g. Cmaj7, F#m7b5, Dsus4, C/E) returning notes, intervals, semitones from root, and MIDI numbers.
- [Music Theory Chord Namer](https://www.zero.xyz/c/music-theory-chord-namer-99196cdf/llms.txt): $0.02/call via x402. Identifies the best chord name, inversion, and alternative names from a set of input notes, treating the first note as the bass.
- [Music Theory Roman Numeral Analysis](https://www.zero.xyz/c/music-theory-roman-numeral-analysis-2b20166b/llms.txt): $0.02/call via x402. Analyzes a chord progression in a given key and returns Roman numeral notation including inversions, borrowed chords, and secondary dominants.
- [Music Theory Interval Calculator](https://www.zero.xyz/c/music-theory-interval-calculator-3115c582/llms.txt): $0.02/call via x402. Calculates the interval between two notes (quality, number, semitones) or finds the note a given interval above or below a starting note.
- [Music Theory Tempo Calculator](https://www.zero.xyz/c/music-theory-tempo-calculator-f7fd0089/llms.txt): $0.02/call via x402. Converts a BPM tempo into delay times and note durations in milliseconds, or averages tap intervals into a steady BPM value.
- [Music Theory Note-to-Frequency Converter](https://www.zero.xyz/c/music-theory-note-to-frequency-converter-3caa6314/llms.txt): $0.02/call via x402. Converts a note name (e.g. C#4, Bb3) or MIDI number to its MIDI value, frequency in Hz, and wavelength in cm, with an adjustable A4 reference pitch.
- [Music Theory Key Signature Lookup](https://www.zero.xyz/c/music-theory-key-signature-lookup-38ebacc0/llms.txt): $0.02/call via x402. Returns key signature details (sharps/flats, accidentals), circle-of-fifths position and neighbours, and relative/parallel keys for any major or minor key.

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

- [Zero catalog index](https://www.zero.xyz/llms.txt)