How to play Tic-Tac-Toe

Tic-Tac-Toe, also known as noughts and crosses or XOX, is the game of three in a row. Two players take turns marking the squares of a grid, one with X and one with O, and the first to complete a straight line of their own marks wins. It is often the very first strategy game people learn, and it is a perfect lesson in looking one move ahead: every move is either an attack, a defence, or a chance you hand to your opponent.

On the classic 3 x 3 board, perfect play from both sides always ends in a draw. That makes the real game a test of accuracy: can you avoid every trap, and can you spot the moment your opponent slips? On skill.games you can also play on two bigger boards where four in a row is needed, which leaves far more room for clever setups.

How to play on skill.games

In the settings popup choose a difficulty (Easy, Normal, Hard or Crazy) and a board (3 x 3, 4 x 4 or 5 x 5), then press PLAY. You play the blue X and you always move first; the computer plays the red O.

• Placing a mark: tap an empty square. You can also press and slide: a faint X shows on the square under your finger, follows it as you move, and is placed where you lift your finger.
• Taken squares cannot be played; a tap there is refused with a little shake.
• The latest mark sits on a tinted square, so you can always see where the computer just played.
• Score line: the top of the screen shows how many marks each side has placed and whose turn it is.
• Easy only: a red outline warns you of any square where the computer could complete its line with its next mark.

The menu button in the top-left corner pauses the game and lets you resume, start a new game or switch the sound on or off. The game is saved at every turn, so an unfinished game can be picked up later with CONTINUE.

When someone completes a line, it is struck through, then the results screen shows the outcome, the number of moves and how the game ended, together with your statistics for that board and difficulty: wins, losses, draws, win rate, current streak and best streak.

Rules

• The board starts empty. You (X) place first, then you and the computer (O) take turns.
• On your turn you place one mark on any empty square. Marks are never moved or removed.
• 3 x 3: three of your marks in a row wins.
• 4 x 4 and 5 x 5: four of your marks in a row wins.
• A line can run across, down or along either diagonal.
• If every square is filled and nobody has a line, the game is a draw.

Strategy tips

• Take the centre. On 3 x 3 the centre square lies on four lines (a row, a column and both diagonals), more than any other square. Corners lie on three, edges on only two.
• Answer a centre with a corner. If the centre is taken against you, a corner is the safe reply. An edge reply gives the first player easy chances to set a trap.
• Look for forks. The winning idea in Tic-Tac-Toe is the fork: one move that creates two separate threats at once. Your opponent can block only one of them.
• Block before you build. Before every move, check whether the computer has two in a line with the third square empty. If it does, block it, unless you can win at once.
• Block forks early. When you defend, ask where the computer could make a fork next turn, and either take that square yourself or force it to answer a threat of yours.
• On the big boards, keep lines open. Four in a row needs space. A line already holding one of the computer's marks is useless to you, so build where your rows, columns and diagonals are still clear.
• Two-way threes win on 5 x 5. Three in a row with both ends free threatens to become four at either end, and only one end can be blocked.

Difficulty levels

• Easy: plays at random about half the time, takes a win when it sees one and often, but not always, blocks yours.
• Normal: always takes a win and always blocks your line, but only looks a couple of moves ahead and plays a random move now and then, so it can walk into a fork.
• Hard: looks much further ahead and never ignores a threat; just occasionally it makes a less accurate move.
• Crazy: searches as deep as it can and never relaxes. On 3 x 3 it plays perfectly and cannot be beaten: a draw is the best possible result, and it chooses the moves that give you the most chances to go wrong. On the bigger boards it is the strongest opponent.

Modes

The Board setting picks the grid:

• 3 x 3: the classic game, three in a row wins.
• 4 x 4: four in a row wins, so only the full rows, columns and the two long diagonals count. Every line can be blocked with a single mark, which makes it a careful, defensive game where draws are common.
• 5 x 5: four in a row wins on a five-square board, so each row, column and diagonal holds two possible lines. There is room to build two threats at once, and games are decided far more often.

Statistics are kept separately for every board and difficulty.