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PlayByKey Music Theory

Official registry Media and design

Chords, scales, progressions, transposition, and MIDI tools for music theory AI agents.

Source code Documentation

What can you do with PlayByKey Music Theory?

Install

Add this to your client's MCP configuration (Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code and others use the same "mcpServers" shape).

NPM package @playbykey/theory-mcp
Claude Code 
claude mcp add playbykey-music-theory -- npx -y @playbykey/theory-mcp@1.6.0
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "playbykey-music-theory": {
            "command": "npx",
            "args": [
                "-y",
                "@playbykey/theory-mcp@1.6.0"
            ]
        }
    }
}

Documentation

From the project's README on GitHub, refreshed weekly. Links open on GitHub.

Contents
  1. Developer Tools
  2. Install
  3. Why @playbykey/theory
  4. Packages
  5. License

Developer Tools

Packages for PlayByKey - see the table below for what's here.

Install

npm install @playbykey/theory
pnpm add @playbykey/theory
yarn add @playbykey/theory
bun add @playbykey/theory

Quickstart and API examples: packages/theory/README.md

Why @playbykey/theory

  • Foundation music theory engine: music theory as code. Modes, keys, intervals, and scale relationships resolved deterministically; one source of truth every app, notation tool, or AI agent can build on.
  • Zero dependencies: no transitive baggage; safe for agents, edge runtimes, and tight bundles
  • Strictly typed: every function's types exported alongside it, no any
  • Agent-ready: copy-paste LLM context prompt and interactive docs
  • Sharps-only notation: one canonical spelling per note (C#, not Db) keeps the Note type safe and unambiguous. Flats are fully supported for both input (parseNote/parseNoteToken accept Db, Eb, Gb, Ab, Bb) and output (getFlats/getEnharmonicLabels), without extending Note itself.

Packages

PackageDescriptionLinks
@playbykey/theoryZero-dependency music theory engine - scales, modes, intervals, chords, progressions, key relationshipsnpm · docs · changelog
@playbykey/theory-mcpMCP server that exposes the theory engine as AI-callable toolsnpm · README
theory-docsStarlight documentation site (private workspace package)live site · README

License

MIT for the repository tooling and @playbykey/theory. See LICENSE. Individual packages may declare their own license in their package.json.

Frequently asked questions

What is PlayByKey Music Theory?

Chords, scales, progressions, transposition, and MIDI tools for music theory AI agents.

How do I install PlayByKey Music Theory?

It runs on your machine. In Claude Code: claude mcp add playbykey-music-theory -- npx -y @playbykey/theory-mcp@1.6.0. For other clients, paste the JSON configuration from this page into their MCP settings.

Does PlayByKey Music Theory need an API key?

Its registry entry lists no required key or secret. Some features may still need an account with the service it connects to.

Is PlayByKey Music Theory open source?

Yes. Its code is on GitHub under the MIT license.

Who maintains PlayByKey Music Theory?

It is published by DigitalBrewLLC. AI.tn lists it but does not maintain or endorse it.

From the official MCP Registry. Listing is not an endorsement: review a server's code and permissions before giving it access to your data.