XO

Setup

A grid of three squares by three, nine empty cells in all. Two players: one marks X, the other marks O.

X always moves first. Online, the app hands out the marks when the room starts and tells you which is yours in the rail above the board; against the bot you take X.

Nothing is hidden and nothing is shuffled. Both players see the whole position at every moment, which is what makes this a pure test of reading ahead rather than of luck.

How to play

Players alternate. On your turn you place your mark in any one empty square. That is the only action in the game: there is nothing to move, nothing to capture, nothing to draw and no way to pass.

A mark, once placed, never moves and is never removed. Every turn permanently uses up a square, so a game lasts at most nine moves and usually fewer.

The aim is three of your own marks in an unbroken line. There are eight such lines on the board — three rows, three columns and the two long diagonals — and any one of them ends the game the moment it is completed.

You may not play into a square that already holds a mark. If it is your turn and an empty square exists, you must fill one.

Play stops the instant a line is made. If all nine squares fill with no line, the game is drawn — which is exactly what two players who never make a mistake will produce, every time.

Controls

Tap an empty square to place your mark. There is no confirmation step and nothing to drag: the tap is the move, and it is sent the moment you lift your finger.

A square that already holds a mark does not respond, and neither does the board while it is your opponent's turn. The rail above the board states whose turn it is in words, so you never have to work it out from the colours.

When the game ends, the three squares of the winning line are highlighted so you can see how it was won rather than having to find it.

Every square is reachable by a screen reader and announces its position and contents — 'top left, empty' or 'centre, X' — so the board can be played without seeing it.

The board does not mirror in Arabic. The top-left square is the top-left square in both languages, because two players sharing one board must be looking at the same thing.

Scoring

There is no score inside a game of XO. The board produces a win, a loss or a draw and nothing else.

On your profile a win pays 10 points, a draw 3 and a loss 1. Those are the smallest awards here, and deliberately so: a game that takes ninety seconds should not out-earn one that takes twenty minutes.

XO is rated and moves the same ladder as chess. That surprises people, and it is on purpose — it is a full-information game with no luck in it at all, so a result between two people says something real about them.

Rating moves only in an online match between exactly two people. Practice against the bot and games on one phone pay nothing and change nothing.

A turn left unplayed for two minutes is forfeited to your opponent, so an abandoned game never sits open forever.

Winning

You win by completing a line of three of your own marks — across a row, down a column, or along either diagonal. The moment the third mark lands the game is over and the line is drawn through it.

If all nine squares are filled and no line has been made, the game is a draw. That is a real result rather than a non-event: it pays both players, and between two strong players it is the normal outcome.

Leaving the match forfeits it, and so does letting a turn expire. Either way the other player takes the win.

The game is completely solved. Neither player can force a win against correct play, so on the hard difficulty the bot cannot be beaten — the best available result against it is a draw, and getting one is the real test.

Tips

Take the centre if it is free; it is part of four of the eight winning lines, where a corner is part of three and an edge only two.

Always block a line where your opponent has two — but check first whether you can complete three of your own, because winning beats blocking.

The strongest plan is a fork: a move that makes two threats at once, which cannot both be blocked. On hard, the bot never allows one and never misses one.

As the second player, answer a corner opening with the centre. Answering with another corner is the mistake that loses this game, and it is the one almost everybody makes.

If you have the centre and your opponent takes a corner, take the opposite corner. It is the move that leaves them no fork to build.