How to play Reversi

Reversi is a game of trapping and turning. Two players share 64 two-coloured discs on an 8 x 8 board, one playing the black side and one the white. Every move must trap at least one line of the opponent's discs between the new disc and another of your own, and every trapped disc turns over to your colour. When neither player can move any more, the one with more discs on the board wins.

The game is famous for its swings: a position that looks hopeless, with only a handful of your discs on the board, can turn into a big win twenty moves later. Counting discs early on tells you very little. What matters is space, the number of moves you have available, and above all the four corners, which can never be turned once they are taken.

How to play on skill.games

In the settings popup choose a difficulty (Easy, Normal, Hard or Crazy) and press PLAY. You play black and you always move first; the computer plays white.

• Legal moves are marked: on your turn every square where you are allowed to play shows a small dark dot.
• Placing a disc: tap a dotted square. You can also press and slide: a faint disc shows on the dotted square under your finger and follows it, and lifting your finger places it there.
• Illegal squares are refused with a short shake.
• Turning over: the trapped discs flip one after another, starting next to the disc you placed.
• The latest disc carries a small red dot, so you can always see where the computer just played.
• Passing happens by itself: if a side has no legal move, the board says so (NO MOVE - YOU PASS or BOT PASSES) and the other side moves again.
• Score line: the top of the screen shows how many discs each colour has on the board and whose turn it is.

The menu button in the top-left corner pauses the game and lets you resume, start a new game or switch the sound on or off. The game is saved at every turn, so an unfinished game can be picked up later with CONTINUE.

At the end the winner's discs light up, then the results screen shows the final disc count and the number of moves, together with your statistics for that difficulty: wins, losses, draws, win rate, current streak and best streak.

Rules

• The game starts with four discs in the centre: two black and two white, placed diagonally.
• Black moves first, then the players alternate.
• A move places one disc of your colour on an empty square so that it outflanks the opponent: in at least one straight line (across, down or diagonally) there must be one or more of the opponent's discs between the new disc and another disc of yours, with no gaps.
• Every line of opponent discs that the new disc outflanks is turned over to your colour, in all directions at once. Discs turned this way do not cause any further turning.
• If you have no legal move, you pass and your opponent plays again. You may not pass while you have a legal move.
• The game ends when neither player can move, usually because the board is full. The player with more discs wins; equal counts are a draw.

Strategy tips

• Take the corners. A disc in a corner can never be outflanked, and it anchors the edges next to it. Most games between good players are decided by who holds more corners.
• Avoid the squares next to an empty corner. The square diagonally inside a corner is the most dangerous one on the board: playing there while the corner is empty usually lets your opponent take it. The two edge squares beside a corner are risky in the same way.
• Fewer discs can be better. In the opening and middle game, flipping many discs often just gives your opponent more choices. Quiet moves that turn one or two discs keep your options open.
• Keep your moves, take away theirs. The player with more available moves is usually winning. Try to leave your opponent with only bad moves, so they are forced to give you a corner.
• Stay inside. Discs next to empty squares (the frontier) give your opponent something to play against. Discs surrounded by other discs are safe and give nothing away.
• Edges are strong but not always safe. An edge disc can only be outflanked along the edge, so stable edge lines are valuable, but an edge disc next to an empty corner can still be turned.
• Count at the end. In the last ten or fifteen moves every disc matters. Look for moves that flip discs that can never be turned back, and remember that a pass can give you two moves in a row.

Difficulty levels

• Easy: plays a random legal move half of the time; otherwise it simply grabs as many discs as it can, which is a classic beginner's mistake.
• Normal: looks two moves ahead and knows which squares are strong, such as corners, and which are dangerous, but it does not think about mobility or the endgame, and plays at random now and then.
• Hard: looks four moves ahead, weighs its own and your available moves, avoids building a wide frontier and plays the last ten squares perfectly.
• Crazy: looks up to eight moves ahead with the same judgement and plays the last twelve squares perfectly. The toughest opponent: you will need to win the corners and the mobility battle well before the end.