Reversi

How to play

Reversi, commonly known by the brand name Othello, is played on an eight-by-eight board that starts with four discs already placed in the center, two of each color. You are black and go first. Tap any highlighted square to place a disc there — a placement is only legal if it traps at least one line of your opponent's discs between your new disc and another disc you already have on the board.

Every opposing disc caught in a trapped line — horizontally, vertically, or diagonally — flips to your color immediately. Play continues until the board is full or neither player has a legal move remaining, and whoever holds more discs at that point wins.

If you have no legal move on your turn, your turn is skipped automatically and passes back to your opponent — you don't choose to pass, and neither does the computer. The board will tell you when this happens.

Playing the computer, or a friend

The computer opponent judges a position by three things: control of the corners and edges, which of you has more legal moves available (more options for you generally means fewer for your opponent), and simple disc count, which matters far less early on than it does once the board is nearly full. Easy looks only a couple of moves ahead. Medium and hard search deeper and are noticeably harder to catch out with a disc count that looks good but isn't backed up by position.

Switching the opponent to two players passes the same board back and forth on one device, with no computer involved. Your game is saved in this browser as you play, so closing the tab does not cost you the position.

Tips for a stronger game

Corners are the single most valuable squares on the board: a disc in a corner can never be flipped, because no line can ever surround it from both sides. Fight for them, and never hand one away for free.

The squares diagonally and directly adjacent to an empty corner are a well-known trap. Playing one often lets your opponent take the corner itself on their next move, which is usually a much worse trade than whatever you gained by playing there. Avoid them until the corner is no longer available to take.

Having more discs on the board early is not necessarily good — a large early lead can leave you with few safe places left to play, handing your opponent easy access to the edges and corners later. Many strong players deliberately keep their disc count low in the middle game and let the position, not the score, do the work.