Cross-Platform Chess Game Development

I am expanding our ambitious chess platform and need the actual game logic built from the ground up so it runs smoothly on iOS, Android and the Web. The visuals, menus and backend services are handled elsewhere—what I require here is the core engine that makes a match possible.

You will take charge of:
• Coding the full chess ruleset (legal moves, check, checkmate, stalemate, threefold repetition, 50-move rule, promotions, castling)
• Providing a clean, platform-agnostic API so my UI teams on Flutter (mobile) and React (web) can call moves, receive board states and animate them in real time
• Ensuring deterministic move validation and accurate FEN/PGN import-export so users can resume or share games
• Implementing time controls and a simple local clock to prepare the ground for eventual online play
- Integrate AI

Acceptance criteria
1. A self-contained module or library that compiles without errors in Xcode, Android Studio and Node/Web builds.
2. Unit-test suite covering every rule edge case.
3. JSON-based move interface documented in a short README.
4. Performance benchmark: validate 1,000 random legal moves in under one second on a mid-range mobile device.

If you have experience with chess engines, cross-platform frameworks, or have shipped similar turn-based games before, your expertise will fit perfectly. Source-control via Git is mandatory; I will invite you to a private repo once we agree on milestones.