Tic-Tac-Toe + Ultimate

With a mouse or touch screen, tap an empty square to place your mark. Against the computer, it replies after a short pause. Use the menus above the board to choose Classic or Ultimate, vs Computer or 2 players, and the computer’s difficulty.

With a keyboard, press Tab to reach the board, use the arrow keys to move between squares and press Enter or Space to play. Press U to undo, H for a hint and N for a new game.

The status line under the buttons always shows whose turn it is. In Ultimate, the small board you must play in is outlined.

Classic

1. X moves first, then players alternate, placing one mark in any empty square.
2. Three of your marks in a row — across, down or diagonally — wins.
3. If all nine squares fill without a line, the game is a draw.

Ultimate

1. The board is nine small Tic-Tac-Toe boards arranged in a 3×3 grid.
2. X may play anywhere for the first move.
3. The square you choose inside a small board sends your opponent to the small board in the same position on the big grid. Play in the top-right square of any small board, and your opponent must play next in the top-right small board.
4. Winning three in a row inside a small board claims that board. A full small board with no winner is claimed by nobody.
5. If you are sent to a board that is already claimed or full, you may play in any open board.
6. Claim three small boards in a row on the big grid to win. If no more moves are possible, the game is a draw.

Classic: take the centre or a corner. The centre touches four winning lines, a corner touches three and an edge only two. If your opponent opens in a corner, take the centre; if they open in the centre, take a corner.

Make two threats at once. A fork creates two lines that each need one more mark, so your opponent can only block one. Most wins against careless players come from a fork.

Always block, then build. Before anything else, check whether your opponent can win next turn.

Ultimate: think about where you send your opponent. Every move is also an instruction. Avoid sending your opponent to a small board where they can win immediately, and try to send them to boards that are already decided or useless to them.

Don’t give away a free choice. Sending your opponent to a finished board lets them play anywhere — a big advantage. Be careful about winning a small board if that leaves its position on the big grid closed in a way that later frees your opponent.

Value the centre board. As in the classic game, the middle small board belongs to the most big-grid lines.

Games of three in a row are ancient: grids for terni lapilli have been found scratched into Roman buildings, and similar games were played across Europe and Asia. The English name “tic-tac-toe” appeared in the late nineteenth century, while British players often call it noughts and crosses. In 1952 it became one of the first computer games when A. S. Douglas programmed a version called OXO on the EDSAC computer at Cambridge. Ultimate Tic-Tac-Toe is far younger: it spread through puzzle blogs and classrooms in the 2010s as a way to keep the simple rules but remove the guaranteed draw.

• Misère (avoid three). The player who completes a line loses.
• Larger grids. On a 4×4 or bigger board, players need four or five in a row, moving toward games like gomoku.
• Moving pieces. In some traditional versions each player has only three pieces and must move one once all are placed.
• Wild Tic-Tac-Toe. Each player may place either an X or an O on any turn, and whoever completes a line of three wins.