3×3 classic

• Two players take turns putting their mark, X or O, in an empty square. X always moves first.
• Get three in a row across, down or diagonally to win.
• If all nine squares fill up with no line of three, the game is a draw. With perfect play on both sides, every game is a draw.

Five in a row

• The same idea on a 15×15 board: the first to get five in an unbroken line (across, down or either diagonal) wins. Six or more in a line also wins.
• Watch out for an open four (four in a row with both ends empty): it can't be stopped. An open three becomes one next turn, so block it early.
• If the board fills up with no winner, the game is a draw.

Modes

• vs Computer: play X (you start), O (the computer starts), or alternate who starts each game.
• Easy plays mostly at random but grabs a win when it sees one. Medium wins and blocks, but a fork (one move that makes two threats at once) can catch it out. Hard never loses at 3×3; at five in a row it blocks your threats and hunts for chains of fours that force a win.
• 2 players: share one device. Name each player and choose whether X alternates between you.

Score and buttons

• The score counts each player's wins and the draws, game after game, until you change the game settings.
• Undo takes back your last move (and the computer's reply). Rematch starts the next game; a game you restart halfway doesn't count. Reset sets the score back to zero.

Controls

• Tap or click an empty square to place your mark.
• Keyboard on the 3×3 board: 1 to 9 pick a square in reading order (1 top left, 9 bottom right).
• On either board, the arrow keys move a highlight and Enter or Space places your mark.