Reversi

Reversi is played on an 8×8 board with discs that are black on one side and white on the other. You place a disc so that it traps a straight line of your opponent’s discs between the new one and another of yours — every trapped disc flips to your colour. When neither player can move, whoever has more discs on the board wins.

It looks like a game about capturing as much as possible, and that instinct is exactly what loses. Discs flip back and forth all game; only the four corners can never be flipped. A player twenty discs ahead at move forty routinely loses by twenty at move sixty.

Play 2 Players on one device, or against the computer. Easy simply grabs the move that flips the most discs, which is the classic beginner mistake made mechanically. Hard searches three moves ahead using a positional table that values corners highly and the squares beside them negatively.

1. Black moves first. The four central squares start filled, two of each colour.
2. Place a disc on any square where it would trap at least one line of your opponent’s discs between it and another of yours. Lines count in all eight directions.
3. Every disc in a trapped line flips to your colour. A move that flips nothing is not legal — legal squares are marked with a small amber dot.
4. If you have no legal move, your turn is skipped automatically and your opponent goes again. If neither player can move, the game ends.
5. The player with more discs on the board wins. The count at the top updates after every move.

One control: click or tap a highlighted square. Squares with no legal move are disabled, so a mis-tap does nothing rather than costing you a turn. The amber dots show every square you may play on the current turn.

Against the computer you always play black and move first. It replies after roughly a third of a second — long enough to see which discs flipped.

There are no keyboard controls and no timer.

• Take corners whenever you can. A corner disc can never be flipped, and it anchors whole edges. This is the single most important idea in Reversi.
• Avoid the squares next to corners. Playing the diagonal square beside an empty corner usually hands that corner to your opponent. Strong players will not touch them.
• Having fewer discs in the midgame is good. Fewer discs means fewer of your pieces available to be flipped, and more legal moves relative to your opponent.
• Play for mobility, not captures. If your opponent runs out of legal moves they must pass, handing you free turns. Restricting their options wins more games than flipping discs.
• Count carefully in the last ten moves. The endgame is where the score actually settles. Up to that point the count is almost meaningless.