Learn Go: Tutorial

Each stone has liberties — the empty intersections directly adjacent to it (up, down, left, right; not diagonal).

- A stone in the center has 4 liberties.

- A stone on the edge has 3 liberties.

- A stone in the corner has 2 liberties.

Connected stones of the same color form a group and share their liberties. A group stays on the board as long as it has at least one liberty.

When you fill all the liberties of an opponent's group, those stones are captured and removed from the board. Captured stones count toward your score at the end.

Here Black has surrounded a white stone on three sides. One more Black stone (at the remaining liberty) would capture it.

On the right, the white stone in the corner has only one liberty left — it is about to be captured.

When a group has only one liberty remaining, it is said to be in atari. This is a warning — on the next move, the opponent can capture that group.

A player whose stones are in atari must decide: extend the group to gain liberties, connect to a friendly group, or sacrifice the stones.

Below, both a single white stone and a two-stone black group are in atari.

Sometimes a capture creates a situation where the opponent could immediately recapture, recreating the previous board position. This would lead to an infinite loop.

The ko rule prevents this: after a single stone is captured, the opponent cannot immediately recapture at that same intersection. They must play elsewhere first (a "ko threat"), then they may recapture on a later turn.

Below, if Black captures at the marked intersection, White cannot recapture on the very next move.

An eye is an empty intersection completely surrounded by stones of one color. The opponent cannot play inside a single eye (it would be suicide), but they *can* fill it if the group has only one eye.

A group with two separate eyes is unconditionally alive — the opponent can never fill both simultaneously, so the group can never be captured.

Below, the black group in the top-left has two eyes and is alive. The white group on the right has two eyes and is also alive.

A false eye looks like an eye but is not truly secure. If the opponent controls key diagonal intersections, they can eventually fill the "eye" because the surrounding stones are not all truly connected.

A group with one real eye and one false eye has only one true eye and is therefore dead — it can be captured.

Below, the black group's left eye at (4,1) is real, but the point at (4,3) is a false eye because White controls the diagonals. Black's group is vulnerable.

Territory consists of empty intersections that are completely enclosed by stones of one color. Only empty points fully surrounded by a single color count as that player's territory.

If an empty area touches stones of both colors, it is neutral (called *dame*) and scores zero.

Below, Black controls territory in the top-left corner, while White controls territory in the bottom-right. The border between them is contested.

This game uses area scoring (Chinese rules). Each player's score equals:

- Stones on the board belonging to that player

- Territory: empty intersections surrounded exclusively by that player's stones

- Komi: White receives 5.5 bonus points to compensate for Black's first-move advantage

The half-point in komi (5.5) ensures there is no draw.

Below, Black has territory in the top rows, White has territory in the bottom rows. White's komi offsets Black's spatial advantage.

The game ends when both players pass consecutively. A player passes when they believe no more profitable moves remain.

After both passes, the board is scored. Dead stones (groups that cannot avoid capture) are removed, then territory and stones are counted.

Below is a finished 9x9 game. Black has territory in the top-left; White has territory in the bottom-right. After adding komi, the final scores determine the winner.

Go has two main scoring systems:

Chinese (area) scoring counts your stones on the board plus the empty territory you surround. Komi is typically 7.5 on a 19×19 board.

Japanese (territory) scoring counts only empty territory plus prisoners captured during the game. Stones on the board do not count directly. Komi is typically 6.5 on a 19×19.

In most situations the results are identical, but they can differ when players play extra stones inside their own territory (which costs a point under Japanese rules but not Chinese).

The board below shows a finished game scored under Japanese rules. Black captured 4 prisoners; White captured 2. Those captures are added to each player’s territory count.

The basic simple ko rule only prevents *immediate* recapture at one point. However, in rare situations (such as triple ko, eternal life, or sending-two-returning-one), a cycle of captures can repeat a board position from many moves ago without ever triggering simple ko.

The superko rule closes this loophole: a player may not make any move that recreates a board position that has occurred previously in the game. The engine tracks every past position and rejects any move that would produce a duplicate.

Below is a position with `koRule: "superko"` active. The position history already contains several past states. If Black tries to recapture at the highlighted points, the resulting board would match an earlier position — so superko forbids it, even though simple ko would allow it.