How to Win at Reversi

Corners first

A disc in a corner can never be turned over: no line runs through a corner with squares on both sides of it. Corners are also the anchors from which you can build rows of discs along the edges that cannot be turned over either. Taking corners, and stopping your opponent from taking them, is the first thing to learn.

The dangerous squares: X and C

The squares touching a corner are where corners are lost. The diagonal ones (b2, g2, b7 and g7) are called X-squares, and the edge squares next to a corner (a2, b1, g1, h2, a7, b8, g8 and h7) are C-squares.

A disc on an X-square gives your opponent a line toward the corner. As soon as they have a disc further along that diagonal, the corner is theirs:

Avoid X-squares unless the corner next to them is already taken, and treat C-squares with care. Once a corner is occupied, the squares around it are ordinary squares again.

Mobility: fewer discs, more moves

The most common beginner mistake is to turn over as many discs as possible every move. In the middle of the game, having many discs usually means having few moves, because there are few of your opponent's discs left to outflank. Strong players do the opposite: they keep their own number of possible moves high and their opponent's low, and let the opponent take discs.

The aim is to leave your opponent with only bad moves, so they have to play onto an X-square, give up an edge or open a corner for you. The Hard computer opponent on this page values exactly this: the difference between its number of moves and yours.

Quiet moves and frontier discs

A frontier disc is one next to an empty square. Every frontier disc of yours is something your opponent can play against, so it gives them moves. A quiet move turns over few discs, ideally ones in the middle that are not next to empty squares, and adds no new frontier. Prefer quiet moves to loud ones that turn over a long line of discs on the outside.

Edges

Edge discs can only be turned over along the edge itself, which makes them more stable than discs in the middle, but an edge is not automatically good. A long edge with gaps lets your opponent wedge a disc in, and a disc next to an empty corner can hand over the corner. Take an edge when it gives you a safe position or forces your opponent into a bad move, not just because it is there.

Parity: getting the last move

Near the end, the empty squares split into separate regions. Having the last move in a region is an advantage, because nobody can answer it. Since the players alternate, a region with an odd number of empty squares tends to give the last move to whoever plays there first. Try to move into odd regions and leave even ones, and count the empty squares before choosing between two moves that look alike.

The endgame: count it out

With about a dozen empty squares left, the number of possible move orders becomes small enough to count. Disc counts finally matter here, and strong players work through the remaining moves exactly. The Hard level does this for the last 12 empty squares when it can finish the count in time, so expect it to play the ending well.

A checklist for each move

1. Can I take a corner? Can my opponent take one after this move?
2. Does this move put a disc on an X- or C-square next to an empty corner?
3. How many moves will my opponent have afterwards, and how many will I have?
4. Does it turn over discs on the outside, creating new frontier discs?

Is Reversi solved?

In 2023 Hiroki Takizawa published a computer analysis, as a preprint, reporting that the standard 8×8 game ends in a draw with perfect play from both sides. On the smaller 4×4 and 6×6 boards, perfect play wins for the second player. None of that helps much over the board: the analysis needed enormous computer time, and human games are decided by the ideas above.

Put them to work: the board at the top of this page plays at three levels. If you are new to the game, start with the rules, with diagrams.