chess-project/LICENSING.md

Licensing Strategy

Overview

This project uses a dual licensing approach based on how the software is built and distributed:

GPL-3.0 License (Web Version)

The web version of Chess Tutor includes Stockfish.js, which is licensed under GPL-3.0. Therefore:

• Source code: GPL-3.0
• Web builds (using LocalEngine): GPL-3.0
• Any distribution that includes Stockfish.js: GPL-3.0

Users can:

• Use the web version for free
• Bring their own API keys (Gemini)
• Run locally with client-side Stockfish

Proprietary License (Mobile Version)

The mobile version (iOS/Android) does NOT bundle Stockfish.js. Instead, it uses:

• RemoteEngine - Makes API calls to a hosted server for chess analysis
• No GPL code is included in the mobile build
• Static export with API-only architecture

Therefore, the mobile app can be distributed under a proprietary license:

• Sold on App Store / Google Play
• Uses hosted API service
• No GPL restrictions apply

How This Works

Code Architecture

// Engine abstraction allows swapping implementations
export interface ChessEngine {
  evaluate(fen: string, depth?: number): Promise<EngineEvaluation>;
  terminate(): void;
}

// GPL-licensed (web only)
class LocalEngine implements ChessEngine {
  // Uses stockfish.js in browser
}

// No GPL dependencies (mobile)
class RemoteEngine implements ChessEngine {
  // Calls API server
}

Build Configuration

Web Build (npm run build):

• Output: output: 'standalone' (Next.js server)
• Includes: API routes with Stockfish
• Engine: LocalEngine (GPL)
• License: GPL-3.0

Mobile Build (npm run build:mobile):

• Output: output: 'export' (static HTML/JS)
• Excludes: API routes (temporarily removed during build)
• Engine: RemoteEngine (proprietary)
• License: Proprietary

Legal Compliance

GPL Compliance (Web)

The web version complies with GPL-3.0:

• ✅ Source code is available
• ✅ GPL license is included
• ✅ Users can modify and redistribute
• ✅ Users bring their own API keys (no lock-in)

Mobile Compliance

The mobile version is NOT a derivative work of GPL code:

• ✅ No Stockfish.js included in build
• ✅ Uses network API calls (not linking)
• ✅ Can be licensed separately
• ✅ Users pay for hosted service

File Structure

chess_tutor/
├── LICENSE              # GPL-3.0 (for source code and web)
├── LICENSING.md        # This file (dual licensing explanation)
├── src/
│   └── lib/
│       ├── stockfish.ts         # GPL-licensed (web only)
│       └── engine/
│           ├── LocalEngine.ts   # GPL-licensed (web only)
│           └── RemoteEngine.ts  # Proprietary (mobile)
├── public/              # Generated data (not in git)
│   ├── openings/*.json  # Fetched at Docker startup
│   └── wikipedia/*.json # Fetched at Docker startup
└── scripts/
    ├── docker-entrypoint.sh     # Fetches data on startup
    └── build-mobile.sh          # Excludes GPL code

Developer Guidelines

Contributing

All contributions to the source code repository are subject to GPL-3.0.

Building for Web

npm run build
npm start
# GPL-3.0 applies

Building for Mobile

npm run build:mobile
# Proprietary license can apply (no GPL code included)

Deploying

Web Deployment:

• Must comply with GPL-3.0
• Must provide source code
• Can be self-hosted for free

Mobile App Store:

• Uses proprietary license
• Connects to hosted API
• Paid app model allowed

Questions?

• Web version: GPL-3.0 applies because Stockfish.js is included
• Mobile version: Proprietary license allowed because no GPL code is bundled
• Source code: GPL-3.0 (contains GPL integration code)

This approach allows:

• ✅ Free web version (GPL-compliant)
• ✅ Paid mobile app (proprietary)
• ✅ Single codebase
• ✅ Legal compliance