diff --git a/.gitignore b/.gitignore
index 20d6b3d..efcace3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,6 +15,7 @@ out/
 
 # Logs
 *.log
+server.log
 npm-debug.log*
 yarn-debug.log*
 yarn-error.log*
@@ -23,4 +24,3 @@ pnpm-debug.log*
 # OS files
 .DS_Store
 Thumbs.db
-
diff --git a/README.md b/README.md
index b3b6f43..ed21cfc 100644
--- a/README.md
+++ b/README.md
@@ -11,9 +11,23 @@ A notepad-playable browser game that combines Tic Tac Toe's line-making goal wit
 - First player to make `4 in a row` wins.
 - If the board fills with no winner, the game is a draw.
 
-## Run
+## Run Multiplayer
 
-Open `index.html` in a browser.
+```powershell
+npm start
+```
 
-No build step is required.
+Then open `http://localhost:3000` in two browser windows. The first two connected players are paired automatically.
 
+Set a different port with:
+
+```powershell
+$env:PORT=4000; npm start
+```
+
+## Notes
+
+- No authentication or user accounts are required.
+- The server keeps games in memory only.
+- If an opponent closes their window, the remaining player sees a disconnect error and waits for a new player.
+- No build step is required.
diff --git a/game.js b/game.js
index 5b286f1..4fac0e2 100644
--- a/game.js
+++ b/game.js
@@ -19,6 +19,7 @@ const resetButton = document.querySelector("#resetButton");
 const xCapturesElement = document.querySelector("#xCaptures");
 const oCapturesElement = document.querySelector("#oCaptures");
 const moveList = document.querySelector("#moveList");
+const networkStatus = document.querySelector("#networkStatus");
 
 let board;
 let currentPlayer;
@@ -26,6 +27,10 @@ let captures;
 let gameOver;
 let moveNumber;
 let winningCells;
+let socket;
+let localPlayer = "";
+let roomId = "";
+let multiplayerState = "connecting";
 
 function createBoard() {
   return Array.from({ length: size }, () => Array(size).fill(empty));
@@ -40,12 +45,80 @@ function setupGame() {
   winningCells = [];
   moveList.innerHTML = "";
   render();
-  setMessage("Trap enemy marks between your marks. First to four wins.");
+}
+
+function connectToServer() {
+  const protocol = window.location.protocol === "https:" ? "wss:" : "ws:";
+  socket = new WebSocket(`${protocol}//${window.location.host}/ws`);
+  setMultiplayerState("connecting", "Connecting to matchmaker...");
+
+  socket.addEventListener("open", () => {
+    setMultiplayerState("waiting", "Connected. Waiting for another player...");
+  });
+
+  socket.addEventListener("message", (event) => {
+    const payload = JSON.parse(event.data);
+    handleServerMessage(payload);
+  });
+
+  socket.addEventListener("close", () => {
+    localPlayer = "";
+    roomId = "";
+    setMultiplayerState("error", "Connection closed. Refresh to reconnect.");
+    render();
+  });
+
+  socket.addEventListener("error", () => {
+    setMultiplayerState("error", "Could not reach the multiplayer server.");
+    render();
+  });
+}
+
+function handleServerMessage(payload) {
+  if (payload.type === "waiting") {
+    localPlayer = "";
+    roomId = "";
+    setupGame();
+    setMultiplayerState("waiting", "Waiting for another player...");
+    return;
+  }
+
+  if (payload.type === "paired") {
+    localPlayer = payload.player;
+    roomId = payload.roomId;
+    setupGame();
+    setMultiplayerState("paired", `You are ${localPlayer}. ${currentPlayer} plays first.`);
+    return;
+  }
+
+  if (payload.type === "move") {
+    applyMove(payload.row, payload.col, payload.player, "remote");
+    return;
+  }
+
+  if (payload.type === "reset") {
+    setupGame();
+    setMultiplayerState("paired", `Game reset. You are ${localPlayer}. ${currentPlayer} plays first.`);
+    return;
+  }
+
+  if (payload.type === "opponent-left") {
+    localPlayer = "";
+    roomId = "";
+    gameOver = true;
+    setMultiplayerState("error", payload.message || "Opponent disconnected. Waiting for a new player...");
+    render();
+    return;
+  }
+
+  if (payload.type === "error") {
+    setMultiplayerState("error", payload.message || "Multiplayer error.");
+    render();
+  }
 }
 
 function render() {
   boardElement.innerHTML = "";
-  boardElement.style.setProperty("--size", size);
 
   for (let row = 0; row < size; row += 1) {
     for (let col = 0; col < size; col += 1) {
@@ -56,7 +129,7 @@ function render() {
       cell.dataset.row = row;
       cell.dataset.col = col;
       cell.setAttribute("aria-label", cellLabel(row, col));
-      cell.disabled = gameOver || board[row][col] !== empty;
+      cell.disabled = !canPlayCell(row, col);
 
       if (winningCells.some(([winRow, winCol]) => winRow === row && winCol === col)) {
         cell.classList.add("winning");
@@ -69,7 +142,7 @@ function render() {
         cell.append(mark);
       }
 
-      cell.addEventListener("click", () => playMove(row, col));
+      cell.addEventListener("click", () => playLocalMove(row, col));
       boardElement.append(cell);
     }
   }
@@ -78,6 +151,14 @@ function render() {
   turnBadge.className = `turn-badge player-${currentPlayer.toLowerCase()}`;
   xCapturesElement.textContent = captures.X;
   oCapturesElement.textContent = captures.O;
+  resetButton.disabled = multiplayerState !== "paired";
+}
+
+function canPlayCell(row, col) {
+  return multiplayerState === "paired" &&
+    !gameOver &&
+    localPlayer === currentPlayer &&
+    board[row][col] === empty;
 }
 
 function cellLabel(row, col) {
@@ -86,41 +167,59 @@ function cellLabel(row, col) {
   return mark ? `${mark} at ${position}` : `Empty cell at ${position}`;
 }
 
-function playMove(row, col) {
-  if (gameOver || board[row][col] !== empty) {
+function playLocalMove(row, col) {
+  if (!canPlayCell(row, col)) {
     return;
   }
 
-  moveNumber += 1;
-  board[row][col] = currentPlayer;
-  const captured = captureFrom(row, col, currentPlayer);
-  captures[currentPlayer] += captured.length;
+  const applied = applyMove(row, col, localPlayer, "local");
+  if (!applied) {
+    return;
+  }
 
-  const win = findWin(currentPlayer);
-  addMove(row, col, captured.length);
+  sendToServer({ type: "move", roomId, row, col, player: localPlayer });
+}
+
+function applyMove(row, col, player, source) {
+  if (gameOver || player !== currentPlayer || board[row][col] !== empty) {
+    return false;
+  }
+
+  moveNumber += 1;
+  board[row][col] = player;
+  const captured = captureFrom(row, col, player);
+  captures[player] += captured.length;
+
+  const win = findWin(player);
+  addMove(row, col, player, captured.length);
 
   if (win.length > 0) {
     winningCells = win;
     gameOver = true;
-    setMessage(`${currentPlayer} wins with four in a row.`);
+    setMultiplayerState("paired", `${player} wins with four in a row.`);
     render();
-    return;
+    return true;
   }
 
   if (isDraw()) {
     gameOver = true;
-    setMessage("Draw. The board is full.");
+    setMultiplayerState("paired", "Draw. The board is full.");
     render();
-    return;
+    return true;
   }
 
-  currentPlayer = opponentOf(currentPlayer);
-  setMessage(captured.length > 0
-    ? `${opponentOf(currentPlayer)} captured ${captured.length}. ${currentPlayer} to play.`
-    : `${currentPlayer} to play.`
-  );
+  currentPlayer = opponentOf(player);
+  const captureMessage = captured.length > 0 ? `${player} captured ${captured.length}. ` : "";
+  const turnMessage = currentPlayer === localPlayer ? "Your turn." : `Waiting for ${currentPlayer}.`;
+  setMultiplayerState("paired", `${captureMessage}${turnMessage}`);
   render();
   flashCapturedCells(captured);
+
+  if (source === "remote" && currentPlayer === localPlayer) {
+    window.navigator.vibrate?.(40);
+  }
+
+  return true;
 }
 
 function captureFrom(row, col, player) {
@@ -200,17 +299,30 @@ function isInside(row, col) {
   return row >= 0 && row < size && col >= 0 && col < size;
 }
 
-function addMove(row, col, captureCount) {
+function addMove(row, col, player, captureCount) {
   const item = document.createElement("li");
   const captureText = captureCount === 0 ? "" : `, captured ${captureCount}`;
-  item.textContent = `${moveNumber}. ${currentPlayer} to ${row + 1},${col + 1}${captureText}`;
+  item.textContent = `${moveNumber}. ${player} to ${row + 1},${col + 1}${captureText}`;
   moveList.prepend(item);
 }
 
-function setMessage(text) {
+function setMultiplayerState(state, text) {
+  multiplayerState = state;
+  networkStatus.textContent = text;
+  networkStatus.className = `network-status ${state}`;
   messageElement.textContent = text;
 }
 
+function sendToServer(payload) {
+  if (!socket || socket.readyState !== WebSocket.OPEN) {
+    setMultiplayerState("error", "Connection lost. Refresh to reconnect.");
+    render();
+    return;
+  }
+
+  socket.send(JSON.stringify(payload));
+}
+
 function flashCapturedCells(captured) {
   for (const [row, col] of captured) {
     const cell = boardElement.querySelector(`[data-row="${row}"][data-col="${col}"]`);
@@ -223,6 +335,16 @@ function flashCapturedCells(captured) {
   }
 }
 
-resetButton.addEventListener("click", setupGame);
-setupGame();
+resetButton.addEventListener("click", () => {
+  if (multiplayerState !== "paired") {
+    return;
+  }
+
+  setupGame();
+  setMultiplayerState("paired", `Game reset. You are ${localPlayer}. ${currentPlayer} plays first.`);
+  sendToServer({ type: "reset", roomId });
+});
+
+setupGame();
+connectToServer();
 
diff --git a/index.html b/index.html
index f31248f..110eead 100644
--- a/index.html
+++ b/index.html
@@ -24,6 +24,8 @@
           <div id="message" class="message">Trap enemy marks between your marks. First to four wins.</div>
         </div>
 
+        <div id="networkStatus" class="network-status connecting" role="status">Connecting to matchmaker...</div>
+
         <div id="board" class="board" role="grid" aria-label="Tictactics board"></div>
       </section>
 
@@ -41,7 +43,7 @@
 
         <div class="rule-card">
           <h2>Rule</h2>
-          <p>Place a mark on an empty cell. Any enemy marks trapped in a straight line between your marks are removed.</p>
+          <p>Open the game in two browser windows. The first two connected players are paired automatically.</p>
         </div>
 
         <ol id="moveList" class="move-list" aria-label="Move history"></ol>
@@ -51,4 +53,3 @@
     <script src="game.js"></script>
   </body>
 </html>
-
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..1e3ba19
--- /dev/null
+++ b/package.json
@@ -0,0 +1,10 @@
+{
+  "name": "tictactics",
+  "version": "0.1.0",
+  "private": true,
+  "description": "A notepad-playable capture tic tac toe browser game with simple WebSocket multiplayer.",
+  "scripts": {
+    "start": "node server.js"
+  }
+}
+
diff --git a/server.js b/server.js
new file mode 100644
index 0000000..19dd510
--- /dev/null
+++ b/server.js
@@ -0,0 +1,284 @@
+const crypto = require("crypto");
+const fs = require("fs");
+const http = require("http");
+const path = require("path");
+
+const port = Number(process.env.PORT || 3000);
+const root = __dirname;
+const clients = new Map();
+const rooms = new Map();
+let waitingClientId = "";
+let nextClientId = 1;
+let nextRoomId = 1;
+
+const mimeTypes = {
+  ".html": "text/html; charset=utf-8",
+  ".css": "text/css; charset=utf-8",
+  ".js": "text/javascript; charset=utf-8",
+  ".json": "application/json; charset=utf-8",
+  ".svg": "image/svg+xml",
+  ".ico": "image/x-icon",
+};
+
+const server = http.createServer((request, response) => {
+  const requestUrl = new URL(request.url, `http://${request.headers.host}`);
+  const pathname = requestUrl.pathname === "/" ? "/index.html" : requestUrl.pathname;
+  const filePath = path.normalize(path.join(root, pathname));
+
+  if (!filePath.startsWith(root)) {
+    response.writeHead(403);
+    response.end("Forbidden");
+    return;
+  }
+
+  fs.readFile(filePath, (error, content) => {
+    if (error) {
+      response.writeHead(404);
+      response.end("Not found");
+      return;
+    }
+
+    const type = mimeTypes[path.extname(filePath)] || "application/octet-stream";
+    response.writeHead(200, { "Content-Type": type });
+    response.end(content);
+  });
+});
+
+server.on("upgrade", (request, socket) => {
+  if (request.url !== "/ws") {
+    socket.destroy();
+    return;
+  }
+
+  const key = request.headers["sec-websocket-key"];
+  if (!key) {
+    socket.destroy();
+    return;
+  }
+
+  const accept = crypto
+    .createHash("sha1")
+    .update(`${key}258EAFA5-E914-47DA-95CA-C5AB0DC85B11`)
+    .digest("base64");
+
+  socket.write([
+    "HTTP/1.1 101 Switching Protocols",
+    "Upgrade: websocket",
+    "Connection: Upgrade",
+    `Sec-WebSocket-Accept: ${accept}`,
+    "",
+    "",
+  ].join("\r\n"));
+
+  addClient(socket);
+});
+
+function addClient(socket) {
+  const id = String(nextClientId);
+  nextClientId += 1;
+
+  const client = { id, socket, roomId: "", player: "" };
+  clients.set(id, client);
+
+  socket.on("data", (buffer) => handleSocketData(client, buffer));
+  socket.on("close", () => removeClient(client));
+  socket.on("error", () => removeClient(client));
+
+  if (waitingClientId && clients.has(waitingClientId)) {
+    pairClients(clients.get(waitingClientId), client);
+    waitingClientId = "";
+    return;
+  }
+
+  waitingClientId = id;
+  send(client, { type: "waiting" });
+}
+
+function pairClients(xClient, oClient) {
+  const roomId = String(nextRoomId);
+  nextRoomId += 1;
+
+  xClient.roomId = roomId;
+  xClient.player = "X";
+  oClient.roomId = roomId;
+  oClient.player = "O";
+
+  rooms.set(roomId, { id: roomId, players: [xClient.id, oClient.id] });
+
+  send(xClient, { type: "paired", player: "X", roomId });
+  send(oClient, { type: "paired", player: "O", roomId });
+}
+
+function handleSocketData(client, buffer) {
+  const opcode = buffer[0] & 0x0f;
+  if (opcode === 0x8) {
+    client.socket.write(Buffer.from([0x88, 0x00]));
+    client.socket.end();
+    removeClient(client);
+    return;
+  }
+
+  if (opcode === 0x9) {
+    client.socket.write(Buffer.from([0x8a, 0x00]));
+    return;
+  }
+
+  const message = decodeFrame(buffer);
+  if (!message) {
+    return;
+  }
+
+  let payload;
+  try {
+    payload = JSON.parse(message);
+  } catch {
+    send(client, { type: "error", message: "Invalid message." });
+    return;
+  }
+
+  if (!client.roomId || payload.roomId !== client.roomId) {
+    send(client, { type: "error", message: "You are not currently paired." });
+    return;
+  }
+
+  if (payload.type === "move") {
+    if (payload.player !== client.player) {
+      send(client, { type: "error", message: "Move rejected for wrong player." });
+      return;
+    }
+
+    relayToOpponent(client, {
+      type: "move",
+      row: payload.row,
+      col: payload.col,
+      player: payload.player,
+    });
+    return;
+  }
+
+  if (payload.type === "reset") {
+    relayToOpponent(client, { type: "reset" });
+  }
+}
+
+function removeClient(client) {
+  if (!clients.has(client.id)) {
+    return;
+  }
+
+  clients.delete(client.id);
+
+  if (waitingClientId === client.id) {
+    waitingClientId = "";
+  }
+
+  if (!client.roomId) {
+    return;
+  }
+
+  const room = rooms.get(client.roomId);
+  rooms.delete(client.roomId);
+
+  if (!room) {
+    return;
+  }
+
+  for (const playerId of room.players) {
+    if (playerId === client.id || !clients.has(playerId)) {
+      continue;
+    }
+
+    const opponent = clients.get(playerId);
+    opponent.roomId = "";
+    opponent.player = "";
+    send(opponent, {
+      type: "opponent-left",
+      message: "Opponent disconnected. Waiting for a new player...",
+    });
+    waitingClientId = opponent.id;
+  }
+}
+
+function relayToOpponent(client, payload) {
+  const room = rooms.get(client.roomId);
+  if (!room) {
+    send(client, { type: "error", message: "Room no longer exists." });
+    return;
+  }
+
+  for (const playerId of room.players) {
+    if (playerId !== client.id && clients.has(playerId)) {
+      send(clients.get(playerId), payload);
+    }
+  }
+}
+
+function send(client, payload) {
+  if (client.socket.destroyed) {
+    return;
+  }
+
+  client.socket.write(encodeFrame(JSON.stringify(payload)));
+}
+
+function decodeFrame(buffer) {
+  const firstByte = buffer[0];
+  const opcode = firstByte & 0x0f;
+  const secondByte = buffer[1];
+  const masked = (secondByte & 0x80) === 0x80;
+  let length = secondByte & 0x7f;
+  let offset = 2;
+
+  if (length === 126) {
+    length = buffer.readUInt16BE(offset);
+    offset += 2;
+  } else if (length === 127) {
+    length = Number(buffer.readBigUInt64BE(offset));
+    offset += 8;
+  }
+
+  let mask;
+  if (masked) {
+    mask = buffer.subarray(offset, offset + 4);
+    offset += 4;
+  }
+
+  const payload = buffer.subarray(offset, offset + length);
+  if (!masked) {
+    return payload.toString("utf8");
+  }
+
+  const decoded = Buffer.alloc(payload.length);
+  for (let index = 0; index < payload.length; index += 1) {
+    decoded[index] = payload[index] ^ mask[index % 4];
+  }
+
+  return decoded.toString("utf8");
+}
+
+function encodeFrame(message) {
+  const payload = Buffer.from(message);
+  const length = payload.length;
+
+  if (length < 126) {
+    return Buffer.concat([Buffer.from([0x81, length]), payload]);
+  }
+
+  if (length < 65536) {
+    const header = Buffer.alloc(4);
+    header[0] = 0x81;
+    header[1] = 126;
+    header.writeUInt16BE(length, 2);
+    return Buffer.concat([header, payload]);
+  }
+
+  const header = Buffer.alloc(10);
+  header[0] = 0x81;
+  header[1] = 127;
+  header.writeBigUInt64BE(BigInt(length), 2);
+  return Buffer.concat([header, payload]);
+}
+
+server.listen(port, () => {
+  console.log(`Tictactics multiplayer server running at http://localhost:${port}`);
+});
diff --git a/styles.css b/styles.css
index a4fc8ad..a0f64d4 100644
--- a/styles.css
+++ b/styles.css
@@ -96,6 +96,12 @@ h1 {
   transition: transform 150ms ease, background 150ms ease;
 }
 
+.icon-button:disabled {
+  opacity: 0.45;
+  cursor: not-allowed;
+  transform: none;
+}
+
 .icon-button:hover {
   background: #eee6d6;
   transform: translateY(-1px);
@@ -136,6 +142,32 @@ h1 {
   text-align: right;
 }
 
+.network-status {
+  margin: 0 0 18px;
+  padding: 10px 12px;
+  border: 1px solid rgba(37, 37, 37, 0.14);
+  border-radius: 8px;
+  color: var(--muted);
+  background: var(--panel);
+  font-weight: 800;
+}
+
+.network-status.paired {
+  color: #31592d;
+  background: #e5f3df;
+}
+
+.network-status.waiting,
+.network-status.connecting {
+  color: #665019;
+  background: #fff3c7;
+}
+
+.network-status.error {
+  color: #8d2525;
+  background: #ffe1df;
+}
+
 .board {
   aspect-ratio: 1;
   width: min(100%, 620px);
@@ -307,4 +339,3 @@ h1 {
     max-height: 180px;
   }
 }
-