Reversi online

Reversi in your browser, no sign-up

This reversi online game uses the standard 8 × 8 board, with a quick 6 × 6 board and a long 10 × 10 board as options. Play the computer at three levels (“Easy”, “Medium”, “Hard”) or pass the phone around with “Two players on this device”. Your game in progress and your statistics are stored in your browser only, so you can close the tab and pick up where you left off.

How to play

1. Pick a “Board” size (8 × 8 by default) and a “Mode”. Against the computer, set the “Level” and choose a side under “You play”: “Black (you move first)” or “White”.
2. Tap any square marked with a dot. Those dots are your legal moves; untick “Show legal moves” if you want to find them yourself.
3. Trapped discs flip, the Black and White counters update and a small red dot marks the last move.
4. With a keyboard, the arrow keys move a cursor across the board and Enter places a disc.
5. “Undo move” takes back your last move (and the computer's reply). “Copy moves” copies the “Moves” list, written in a1 to h8 notation.

The rules this game follows

• Setup: four discs in the center, White on d4 and e5, Black on d5 and e4. Black moves first.
• Legal move: you place a disc on an empty square so that, in at least one straight line (across, down or diagonally, 8 directions in all), it traps an unbroken row of opposing discs against one of your own.
• Flipping: every trapped disc flips, in every direction at once. A single move can flip discs along a row, a column and a diagonal together.
• Passing: if you have no legal move, you must pass. The game does it for you and says so. You can never pass while a move is available.
• End of game: play stops when neither side can move, whether or not the board is full. The player with more discs wins; a tie is possible.

A worked example on 8 × 8: Black has exactly 4 opening moves, d3, c4, f5 and e6, and they are all mirror images of each other. After d3 the disc on d4 flips, making the score 4 to 1. White then has 3 replies (c3, e3 or c5), each of which levels the score at 3 to 3. Counting every line of play, there are 12 possible positions after two moves, 56 after three and 244 after four.

How the three computer levels play

“Easy” picks moves at random, with a slight bias toward good squares, which makes it a gentle opponent for learning the rules. “Medium” grabs whichever square scores highest on a table of square values (corners high, squares next to corners low) but never looks ahead. “Hard” searches several moves deep, weighing mobility, corners and discs that can no longer be flipped. Once about a dozen empty squares remain on 8 × 8, it works out the endgame exactly, so it rarely throws away a won position.

A game with a long history

Reversi first appeared in England in the 1880s and was soon a popular parlor game. In the 1970s a version with fixed rules and the central starting position you see here took off in Japan, and it is now played in tournaments around the world.

Strategy tips that actually work

• Corners (a1, h1, a8, h8): a disc in a corner can never be flipped. Taking corners is the main goal.
• X and C squares: the squares diagonally next to a corner (b2, g2, b7, g7) and those beside it on the edge (a2, b1, g1, h2, a7, b8, g8, h7) tend to hand the corner to your opponent. Stay off them while the corner is empty.
• Mobility: having lots of discs in the middle game is rarely an advantage. Keep your own options open and squeeze your opponent's until they are forced into a bad square.
• Edges: an edge anchored to a corner gives you stable discs, but a lone disc on an edge can be trapped.
• Parity: near the end, try to make the last move in each empty region, so your opponent has nothing to answer with.

FAQ

What happens if I have no legal move?

You pass automatically and your opponent moves again. The message says so and “pass” appears in the move list. If both players are stuck, the game ends and the discs are counted, even with empty squares left.

Why does the computer let me take so many discs early on?

On “Hard” it focuses on limiting your moves and winning corners. The disc count only matters at the very end, and having fewer discs in the middle game is often the stronger plan.

Is my game saved?

Yes, on this device and in this browser only. Come back later and the game resumes at the same move. Your won, lost and drawn totals are kept the same way, and “Reset” clears them.

Why play on 6 × 6 or 10 × 10?

A 6 × 6 game lasts 32 moves at most, ideal for a short break or for practicing endgames. The 10 × 10 board allows 96 moves and longer battles. The rules and the central setup stay the same.