Thiri

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Give your AI real music theory. THIRI is the deterministic music theory MCP server + API for AI builders — it lets Claude, Cursor, or any MCP agent analyze chords, run roman-numeral analysis, generate voicings, and reharmonize progressions with answers that are computed, not guessed.

LLMs hallucinate music theory: wrong notes, fake roman numerals, voicings that don't voice-lead. THIRI is a deterministic engine (pitch-class-set theory over ℤ/12) behind a hosted API — so C7sus4 keeps its suspension, Caug spells C E G#, and "Coltrane changes on Dm7 G7 Cmaj7" returns Cmaj7 Ab7 Abmaj7 E7, every time.

Downstream of Suno / Udio or any generator? Wrap the output and get a correct chord chart your agent can trust. And unlike tonal.js or music21, THIRI is hosted and agent-native (no install, any language) — and it reharmonizes and voice-leads, not just looks chords up.

⭐ If this is useful, star the repo — it helps other musicians and agent builders find it.

Musicians: 2-minute setup (no code)

1. Get a free key at build.thiri.ai/developers
2. In Claude: Settings → Connectors → Add custom connector → URL https://mcp.thiri.ai/mcp → paste your sk_live_ key
3. Ask Claude: "Reharmonize Dm7 G7 Cmaj7 with Coltrane changes."

That's it — no install, no config file. Builders: full install options (Claude Code, Desktop config, raw HTTP) are below.

What you can ask

"Analyze Dm7b5 in C." → iiø7, half-diminished, borrowed predominant, + scale options "What notes are in C7sus4?" → C F G Bb (the suspension survives) "Give me a rootless Cmaj7 voicing, then voice-lead into Dm7." → voicings + a voice-leading score "Reharmonize Dm7 G7 Cmaj7 with Coltrane changes." → Cmaj7 Ab7 Abmaj7 E7

Tools

Tool	What it does
analyze_chord	Chord → root, quality, intervals, roman numeral & harmonic function (secondary dominants, modal-interchange labels)
resolve_chord	Chord → spelled notes (enharmonically correct), frequencies, MIDI, scale recommendations
generate_voicing	Instrument-ready voicings (rootless/bill_evans, shell, triad, pad, guide-tones, drop-2/3); pass previousNotes for a voice-leading score; colorPreferences for explicit tensions
reharmonize	Progression reharmonization — 8 techniques: tritone_sub, ii_v_insertion, modal_interchange, diminished_passing, secondary_dominant, chain_of_dominants, coltrane_changes, backdoor (or auto)
conduct_band	Natural-language band conduct → lanes + MIDI (hosted MCP v0.3+)

Runs on the v2 grid engine — correct sus chords, real triads, enharmonic spelling, all altered dominants — with request timeouts, quota reporting, and structured errors.

Conductor & composition companions (Desktop only)

For hear-it agent loops (conduct → server-side render → WAV through your speakers), add a second local server alongside hosted theory tools:

{
  "mcpServers": {
    "thiri": {
      "command": "npx",
      "args": ["-y", "@bluesprincemedia/thiri-mcp"],
      "env": { "THIRI_API_KEY": "sk_live_your_key" }
    },
    "thiri-conductor": {
      "command": "npx",
      "args": ["-y", "@bluesprincemedia/thiri-mcp", "thiri-conductor-mcp"],
      "env": { "THIRI_API_KEY": "sk_live_your_key" }
    },
    "thiri-composition": {
      "command": "npx",
      "args": ["-y", "@bluesprincemedia/thiri-mcp", "thiri-composition-mcp"]
    }
  }
}

Bin	Tools
thiri-conductor-mcp	conduct_band, render_audio (server-side Csound via POST /v2/render), play_audio, search_csound_corpus
thiri-composition-mcp	Composition IR tools + play_composition (fluidsynth preview)

Rendering runs server-side as of v0.5.0 — no Csound install needed. Proof: npm run test:conductor · live docs: build.thiri.ai/lab/conductor-mcp · agent recipes.

Conductor Agent (vibe compose)

End-to-end persona for local vibe composition — skill, CLI, and Band dashboard panel:

Entry	Command / path
Cursor skill	Copy THIRI/lab/skills/thiri-conductor-agent/SKILL.md → ~/.cursor/skills/thiri-conductor-agent/SKILL.md
CLI	cd thiri-mcp && npm run conductor:vibe -- "gospel ballad in F minor"
Dashboard	npm run dev:studio → localhost:5173/band → Vibe Conduct panel
Lab proof	build.thiri.ai/lab/conductor-agent

Dual MCP config above + mapConductResultToStudioModules after each conduct_band. Last CLI render writes ~/.thiri/conductor-last.json (local only, not committed).

Flagship agent recipe (analyze → conduct → render → critique)

Paste in order after dual MCP config above:

1. Analyze — "Analyze Dm7 G7 Cmaj7 in key C with analyze_chord; summarize roman numerals and tension."
2. Conduct — "conduct_band: warm Rhodes pad, walking bass, brush drums, 8 bars medium swing in C."
3. Render — "render_audio from the conduct result at tempo 120."
4. Critique — "play_audio; critique voice-leading and register balance; suggest one revision."

Full prompts: build.thiri.ai/lab/agent-recipes

Hosted vs local boundary

Surface	Audio render
mcp.thiri.ai / hosted connector	No — theory + conduct_band lanes only
Local thiri-conductor-mcp	Yes — WAV rendered server-side (POST /v2/render), played locally; no Csound install needed

Install

Get a free key at build.thiri.ai/developers, then pick a path:

Claude Desktop / web / mobile — hosted (one-click custom connector, nothing to install): Settings → Connectors → Add custom connector → URL https://mcp.thiri.ai/mcp → paste your sk_live_ key on the consent page. Same 5 tools, same key, same quota — no config file, no npx.

Claude Code (one line):

claude mcp add thiri --env THIRI_API_KEY=sk_live_your_key -- npx -y @bluesprincemedia/thiri-mcp

Claude Desktop (claude_desktop_config.json):

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

Prefer raw HTTP? (no MCP needed)

The same engine is a plain REST API:

curl -X POST https://chords.thiri.ai/v2/analyze \
  -H "Authorization: Bearer YOUR_KEY" -H "content-type: application/json" \
  -d '{"chord":"Dm7b5","key":"C"}'

Five endpoints: /v2/analyze, /v2/resolve, /v2/voicing, /v2/reharmonize, /v2/conduct. See openapi.yaml.

Environment variables

Variable	Default	Description
THIRI_API_KEY	(none)	Bearer token (sk_live_…) — get one at build.thiri.ai/developers
THIRI_API_URL	https://chords.thiri.ai	API base (override only for local dev)

Development

npm install && npm run build && npm start

License

PolyForm Noncommercial 1.0.0 — © 2026 Blues Prince Media. Free for personal, research, and noncommercial use; commercial use requires a license ([email protected]). See LICENSE. Versions published at or before v0.5.0 remain under the MIT/PolyForm dual license they shipped with.

As of v0.5.0 the composition engine and Csound renderer run server-side behind the hosted API (POST /v2/compose, POST /v2/render); their source no longer ships in this package.