🎷 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.

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) |

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

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. 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

MIT — © 2026 Blues Prince Media. The client is open; the engine is a hosted service.