🎷 THIRI Chord Intelligence — MCP Server

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.

Related MCP server: Music MCP

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

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

Local Csound MCP (Desktop only)

For hear-it agent loops (conduct → Csound score → WAV), 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"]
    }
  }
}

Requires Csound CLI on PATH for WAV render. 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:

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 — "build_csound_score from lanes, then render_csound_wav 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

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 4 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"}'

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

Environment variables

Development

npm install && npm run build && npm start

License

Dual-licensed — © 2026 Blues Prince Media:

• Client / MCP glue (root, src/, *-server.mjs, tests, docs): MIT — open.

• vendor/ engine (THIRI composition engine + Csound core): PolyForm Noncommercial 1.0.0 — source-available, no commercial use or resale. See vendor/LICENSE.md. Commercial licensing: api@bluesprince.ai.

The composition engine is being migrated behind the API (hosted service); the Csound renderer to a container render service. Until that ships, the engine source lives here under the noncommercial terms above rather than MIT.