How to play Reversi
Reversi is played on an 8 × 8 board with discs of two kinds. Place a disc so that it traps one or more straight lines of the other side’s discs between it and another of yours, and every trapped disc turns over to your side.
Play the computer on Easy, Medium or Hard, or pass the mouse to a coworker. When neither side can move, whoever has more discs wins.
Rules
- The game starts with four discs crossed in the centre. Player 1 has the solid discs and moves first; against the computer, that is you.
- A move must trap at least one line of the other side’s discs, across, down or diagonally and with no gaps, between the new disc and one of yours. Every line it traps turns over at once.
- If you have no legal move you pass, and the other side plays again. You can’t pass while you have a move.
- The game ends when neither side can move, usually once the board is full. Any empty squares left go to the winner, as in tournaments.
- Against the computer a win scores its margin: your discs minus the computer’s. Each level keeps its own best and win streak. A new game started before the end counts as a loss.
- Undo takes back your last move and the computer’s reply; a game with an undo is saved but not ranked. Dots mark the squares you can play (M hides them), a red mark shows the last disc placed, and each mode keeps its game in progress in this browser.
Controls
- Click / tap a square
- Place a disc there
- Arrows / WASD
- Move the cursor
- Enter / Space
- Place a disc at the cursor; after a game, start the next
- Z / U / Backspace
- Undo (Ctrl+Z too)
- M
- Show or hide the legal-move dots
- N
- New game (press twice to leave a game in progress)
Tips
- Take corners when you can, and keep off the squares diagonally inside an empty corner. A disc on a corner can never be turned over, and it anchors the edges either side of it.
- Don’t grab discs early. Having fewer discs in the opening usually leaves you more moves later, and a side that runs out of moves has to give up corners.
- Prefer quiet moves that flip few discs, and flip discs in the middle rather than on the outside. Every disc of yours next to an empty square is a way in for the other side.
Reversi strategy
Know your opponent
Easy plays a random legal move about three times in ten and otherwise the one that turns the most discs, with a slight pull towards corners. It walks onto the squares next to corners, so give it the chance. Medium searches two moves ahead with some noise and Hard seven; both value corners most, then mobility and quiet moves. Hard also counts out the last fourteen squares exactly, so a lead built late is hard to keep against it.
Mobility beats material
Most games are decided by how many moves each side has, not how many discs. Moves that flip a single inside disc keep your options open and take the other side’s away. When your opponent has only bad moves left, usually next to a corner, the corner becomes yours. Count the dots: if a move leaves you more legal moves than before and the other side fewer, it is usually a good one.
Edges and the squares by the corners
The squares diagonally inside a corner, the X-squares, are the most dangerous on the board: a disc there often hands over the corner. The edge squares right next to a corner (C-squares) are risky too while that corner is empty. An edge is good when it can’t be attacked from both ends; a lone disc in the middle of an empty edge can often be wedged.
Parity and the score
Near the end the board breaks into small empty regions. Playing the last move in a region usually gains discs, so try to leave regions with an even number of empty squares for the other side to open. The score is the final margin with empty squares going to the winner, so wiping out every enemy disc scores 64 however early it happens, and finishing a won game cleanly with a few extra discs moves you up the board.
About Reversi
Reversi was invented in England in the 1880s; Lewis Waterman and John W. Mollett both claimed it, each calling the other a fraud. Ravensburger published it in Germany in 1893. In 1971 Goro Hasegawa in Japan patented a version with a fixed starting position, and as Othello it became the form played in tournaments around the world.
Windows 1.0 shipped with Reversi in 1985, and in 1997 the program Logistello beat the world champion Takeshi Murakami six games to none. The computer here is simpler: Easy grabs the most discs, Medium searches two moves ahead and Hard seven, weighing corners, mobility and exposed discs, and from fourteen empty squares Hard calculates the rest of the game to the end.
Questions
Is Reversi the same as Othello?
Almost. Othello is a trademarked version of Reversi that always starts with four discs crossed in the centre, which is how this game starts too. Early Reversi let the players place the first four discs themselves.
What happens if I can’t move?
You pass, and the other side moves again. The game ends only when neither side has a move.
How strong is Hard?
It searches seven moves ahead and plays the last fourteen squares perfectly. In our simulated games it beat Medium every time, usually by more than 40 discs. Expect a few defeats before your first win.
How is the score worked out?
Only wins against the computer score: your discs minus the computer’s at the end, with any empty squares counted for you. On Medium the Expert level is 12 and the Pro level 36; on Hard they are 6 and 24.
