Two players, black and white stones, and a board of lines. You take turns placing a stone where the lines cross, and the one who surrounds more of the board wins. Four thousand years old, the rules fit on a card — and nobody has ever got to the bottom of it.
Free, no sign-up — play the house’s regulars or invite a friend.
Placing stones
Black plays first. Tap a point where two lines cross to put your stone there — it never moves again. (With Confirm each move on, tap once to see it and again to place it.) The game here is on a 9×9 board: quick, about fifteen minutes, and every stone counts.
Liberties and capturing
The empty points right next to a stone (up, down, left, right — not diagonally) are its liberties. Stones of one colour side by side are a group and share theirs. Fill a group’s last liberty and it’s captured: off the board, into your lid. A group with one liberty left is in atari — save it or lose it.
Two rules about where you may play
You can’t play where your stone would have no liberties at all — unless it captures something, which gives it some. And ko: when one stone takes one stone and could be taken straight back, the other side has to play somewhere else first. The board may never repeat a position.
Life and eyes
A group with two separate empty points inside it — two eyes — can never be captured: you can’t fill both at once. That’s what living means. A group that can’t make two eyes, surrounded, is dead, even before it’s taken off.
Passing and the count
When there’s nothing left worth a stone, Pass. Two passes in a row end the game. Then the dead stones come off (the engine marks them — tap a group to change it) and the board is counted: your stones plus the empty points you surround. White gets 7½ points of komi for going second. Disagree about what’s dead? Play on and settle it on the board — under this way of counting, playing inside your own area costs you nothing.
Who’s at the board
Five regulars, from beginner to expert: Dot, Rufus, Margot, Old Sol, The Abbot. All of them play with the house engine, a neural network that learned Go by playing itself nearly twenty thousand games; the stronger ones read further ahead. Hint shows a good move and Undo takes one back — against all but the Abbot. Not ready for an even game? Take 2 to 4 stones of handicap: they’re on the board before White’s first move.
Your rating
Every even game you finish moves your rating (the Elo way: beat someone rated above you and you gain more; lose to someone below and you drop more). Everyone starts at 1200. The regulars are rated too, measured by playing them against each other — the Abbot is 1940 — and each card shows your chances against them. Handicap games aren’t rated.
How well you played
When a game ends the engine reads it again, move by move. Each of your moves is measured against its best by the points it gave up, and graded: best or fine, an inaccuracy (yellow), a mistake (orange) or a blunder (red). Your game in one number: the points you gave up per move — lower is better. Review the game to step through it on the board: your move in blue, the engine’s in gold, the line it expects, and your chances across the whole game. The last twenty games are kept on this device.
Learning as you play
Area shows who the engine thinks each point will belong to. Turn on the Tutor (Settings) and before a mistake stands it says so — what it gives up and what the engine would play — and you can take it back. Turn on Show the win chances for your chances and who leads, after every move.
Tips
Corners first, then the sides, then the middle: walls on two edges make territory cheaply.
Count liberties in a fight. The group with more of them usually wins it.
A group with one eye is a group in trouble. Make the second before you go elsewhere.
Review your losses: the big red dots on the graph are where the game turned.