Deterministic music-theory API + MCP for AI builders

Your AI hallucinates chords. THIRI returns the correct ones.

Analyze any chord, get its roman-numeral function, generate idiomatic voicings, and reharmonize whole progressions — over a REST API or an MCP server your agent calls directly. Computed from music theory, never guessed.

Tap a chord below and hear it — voiced, spelled, and explained. No signup, no key. Then build with the same engine.

▶ Hear it now For developers →

Hear it now · no signup, no key

Tap a chord. Hear THIRI voice it.

Each chord plays live in your browser and gets spelled out — its notes, its Roman-numeral function, and the scale it comes from. Computed from music theory the instant you tap, never guessed.

Cmaj7 Imaj7

Notes CEGB

Scale CDEFGAB

Mode C Ionian

This is the same answer your code gets back from chords.thiri.ai — same notes, same function, same voicing logic. The toy and the API run the identical theory.

Play the full instruments → Make your own with AI → Get a free key → API & MCP docs →

THIRI is to music theory what cURL is to HTTP — the layer so reliable that developers stop thinking about it and just build.

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Every music AI app eventually gets a chord wrong and nobody on the team can hear it — THIRI is the engine that guarantees they never ship that moment.

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It lets any AI agent comp like a jazz musician — correct voicings, correct spellings, correct reharmonizations — without needing a musician on the engineering team.

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Generative models can build the audio, but they still need something to tell the model what Db7 actually is — that's THIRI.

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Every music AI company is hand-rolling chord logic in a utils file somewhere — T.H.I.R.I. replaces that file with four endpoints and an MCP server that's already been tested against real charts in real keys.

POST /v2/resolve { "chord": "Cm7" } { "notes": ["C","Eb","G","Bb"], "midi": [60,63,67,70], "scales": [{"name":"Dorian","role":"primary"}] }

For Developers

Four REST endpoints. Analyze chords from symbols or notes, return roman-numeral harmonic function, generate idiomatic voicings, reharmonize progressions. Bearer auth, live at chords.thiri.ai. Free tier: 1,000 calls/mo.

See the API

{ "mcpServers": { "thiri": { "command": "npx", "args": ["-y", "@bluesprincemedia/thiri-mcp"] } } }

For Agent Builders

One-click hosted MCP — add mcp.thiri.ai/mcp to Claude or Cursor connectors, no install. Or run it locally via npx. Same auth, same four endpoints.

MCP Quickstart

Play THIRI

Hear reharmonization, conduct a band, run Helix, or sing through the vocoder — live in the browser. Same engine as the API.

Try the demos