MCP-to-MCP Tic-Tac-Toe

Instructions

Implementation Reference

• server.js:87-131 (handler)

  The implementation of the `make_move` tool handler, which manages the Tic-Tac-Toe game state, validates moves, and coordinates turn-taking.

  srv.registerTool("make_move", {
    description: "Place your mark on the tic-tac-toe board. Positions: A1, A2, A3, B1, B2, B3, C1, C2, C3.",
    inputSchema: { move: z.string().describe("Board position (e.g. A1, B2, C3)") },
  }, async ({ move }, extra) => {
    const sid = extra.sessionId;
    const heartbeat = () =>
      srv.sendLoggingMessage({ level: "info", data: `Waiting for opponent...\n${render(game?.board || [])}` }, sid).catch(() => {});
  
    if (!game) {
      game = createGame(sid);
      game.waiter = null;
      const r = place(game.board, move, "X");
      if (r.err) { game = null; return txt(r.err); }
      game.board = r.board;
      game.turn = "O";
      game.waiter = waitForOpponent(heartbeat);
      const oppMove = await game.waiter.promise;
      if (!oppMove) { game = null; return txt("Opponent didn't respond in time. Game abandoned."); }
      return endTurn(game, oppMove, "X");
    }
  
    const mark = assignPlayer(game, sid);
    if (!mark) return txt("Game in progress. Try again later.");
  
    if (game.turn !== mark)
      return txt(`Not your turn yet. Current board:\n${render(game.board)}\nYou are ${mark}. Call make_move after opponent plays.`);
  
    const r = place(game.board, move, mark);
    if (r.err) return txt(`${r.err}\nBoard:\n${render(game.board)}\nYou are ${mark}. Call make_move again.`);
    game.board = r.board;
    game.turn = mark === "X" ? "O" : "X";
  
    const w = winner(game.board);
    if (w) {
      if (game.waiter) game.waiter.resolve(move);
      markFinished();
      return txt(`Placed ${move.toUpperCase()} as ${mark}. Game over — ${formatWin(w)}\n${render(game.board)}`);
    }
  
    if (game.waiter) game.waiter.resolve(move);
    game.waiter = waitForOpponent(heartbeat);
    const oppMove = await game.waiter.promise;
    if (!oppMove) { game = null; return txt("Opponent didn't respond in time. Game abandoned."); }
    return endTurn(game, oppMove, mark);
  });

• server.js:223-226 (registration)

  The registration of the `make_move` tool for the stdio proxy transport.

  stdioSrv.registerTool("make_move", {
    description: "Place your mark on the tic-tac-toe board. Positions: A1, A2, A3, B1, B2, B3, C1, C2, C3.",
    inputSchema: { move: z.string().describe("Board position (e.g. A1, B2, C3)") },
  }, async ({ move }) => proxyMove(proxyUrl, move));