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Play Go online on the three standard boards: 9 × 9 to learn, 13 × 13 as a step up and 19 × 19 for the full traditional game. Play against the computer, or pass the device back and forth with a friend. The game is called weiqi in China and baduk in Korea; the rules are the same everywhere.

How to play

1. Pick the "Board" and the "Mode". Against the computer, also set the "Level" and "You play". Black moves first.
2. Tap an intersection to place a stone. A ring marks the last move; with a mouse, a see-through stone shows where you are about to play. Keyboard: arrow keys, then Enter.
3. "Pass" hands the turn over. Two passes in a row end it.
4. "Undo move" takes back your last move and the computer's reply. "Resign" asks you to confirm first.

The rules, step by step

• Placing: players take turns putting one stone on an empty intersection. Stones never move afterwards.
• Liberties: the empty points directly next to a stone (up, down, left, right). Touching stones of one colour form a group and share their liberties.
• Capture: a group that loses its last liberty is removed and its stones become captures. One stone can capture several groups at once.
• No suicide: you may not play where your stone would have no liberties, unless the move captures something, because the capture immediately frees a liberty.
• Ko: you may not instantly retake a single stone that has just captured a single stone, since that would repeat the previous position. Play elsewhere first, then the retake is allowed. More generally, no earlier position may come back with the same player to move.
• End: when no move gains anything, both players pass. Dead stones are removed and the board is counted.

Scoring: territory or area

After two passes, the tool suggests which stones are dead. Tap a group to switch it between dead and alive, then press "Accept the score". "Territory (Japanese)" counts the empty points surrounded only by your stones, plus your captures, plus the opponent's dead stones. "Area (Chinese)" counts your living stones plus your territory. Komi, 6.5 points by default, goes to White to make up for Black's first move; the half point rules out ties.

A worked 9 × 9 example: Black holds the whole D column, White the E column. A dead white stone sits on B5, a dead black stone on H5, and Black has played one extra stone at C7 inside its own area. Territory: Black has 26 empty points in columns A to C plus 1 dead white stone, 27 in total; White has 36 points in columns F to J plus 1 dead stone plus 6.5 komi, 43.5. White wins by 16.5. Area: Black has 10 stones plus 26 points, 36; White has 9 stones plus 36 points plus 6.5 komi, 51.5. White wins by 15.5. The stone at C7 costs a point under territory, nothing under area.

When the players differ in strength, the weaker one takes Black and gets 2 to 9 "Handicap" stones on the traditional star points (hoshi). White then moves first and komi drops to 0.5, which you can change. Under Chinese scoring, White also receives 1 point per handicap stone.

Starting out on 9 × 9: five tips

• Open in the centre or on the third line (C3, E5, G7). The first line is worth almost nothing early on.
• Keep your stones connected: two separate groups are two targets.
• Count liberties before a fight. The group with more of them usually wins the race.
• A group lives with two eyes, two separate empty points it surrounds on its own: the opponent can fill neither.
• Don't play inside territory you have already sealed: under Japanese scoring each such stone costs you a point.

How strong is the computer?

The computer plays thousands of random games to the end and keeps the move that wins most often. It thinks for 0.3 seconds on "Easy", 1.5 on "Medium" and 4 on "Strong". On 9 × 9 it punishes careless play, yet an experienced club player will still beat it. On 13 × 13 it holds up reasonably well. On 19 × 19 it is playable but weak, so a human opponent is the better choice there. It resigns when it judges the game lost, and after you pass it passes too if it believes it is ahead.

Frequently asked questions

How do I save a game or come back to it later?

The current game stays on this device and resumes at the same move. "Download .sgf file" saves it in SGF, the standard format most Go programs open; "Copy SGF" puts it on your clipboard.

Can I import a game?

Yes. Paste an SGF and press "Import this SGF", or use "Open an .sgf file". Board size, komi, handicap stones and the main line of moves are read; comments and variations are skipped.

Why was my move refused?

The message tells you: the point is taken, the move would be suicide, or it would retake a ko straight away.

What if the dead stones are marked wrongly?

Tap the group in question: its status flips and the table updates at once. You can also undo the last pass and settle the matter on the board.