♟️ 6D Chess

Multiverse chess with timeline branching. Make a move to create alternate realities.

Rules

On top of normal chess:

• Cross-timeline moves — any piece except the king can jump to the same square on another board and land on a square it could reach from there. Both boards must be at the same move count with the same side to move, the landing can't capture, and the move must not leave your king in check on either board. A pawn landing on the last rank promotes to a queen.
• Time travel — queens, rooks, bishops and knights can travel back to an earlier position on their board where it was their side's turn. This spawns a new timeline. Leaving must not expose your king, and the arrival must be legal.
• The game ends when every timeline has finished (checkmate, stalemate or draw).

Development

npm install
npm run dev        # build and serve on http://localhost:8000/
npm run watch      # rebuild on change

The app is static: index.html, css/, dist/bundle.js and lib/ (Three.js, chess.js, Stockfish WASM). It works from any path (/, /chess, /chess/, /6Dchess/).

Tests

npm run lint       # strict type check
npm run test:unit  # rules, FEN utilities and a randomized multiverse fuzz test (Node)
npm run test:e2e   # Playwright: plays the real app in headless Chromium, incl. CPU self-play
npm test           # both

E2E screenshots land in test-results/screens/. CI runs everything on each pull request; pushes to main deploy to GitHub Pages.

Code map

File	What it does
src/rules.ts	Pure multiverse move rules (validates and plans cross-timeline / time-travel moves)
src/gameUtils.ts	FEN helpers and validation
src/game.ts	Game controller: timelines, UI, CPU player
src/board3d.ts	Three.js scene: boards, history stacks, connection lines, effects
src/stockfish.ts	Stockfish worker wrapper used by the CPU player