Reversi Strategy: How to Win

There is no formula that wins every game of Reversi, but there is a short list of principles that strong players follow and beginners almost always break. Learn them and you will beat most casual players immediately, and start troubling the Hard AI and above in ReversiAI.

Last updated: 2026-10-09

1. Corners can never be flipped, so corners are worth the most

The four corners (a1, h1, a8, h8) are the only squares that can never be outflanked: there is no line through a corner with squares on both sides. A corner disc is permanently yours, and discs that extend from it along the edges gradually become permanent too. These are called stable discs.

Much of the midgame is a fight over who gets corners and who is forced to give them away.

2. While a corner is empty, never play the X-square next to it

X-squares are the four squares diagonally adjacent to a corner: b2, g2, b7, g7. Playing an X-square while the corner is still empty almost always lets your opponent outflank it along the diagonal and take the corner in the process. It is the single most common way beginners lose.

C-squares are the eight squares orthogonally adjacent to a corner (a2, b1, g1, h2, a7, b8, g8, h7). They are less dangerous than X-squares but can still hand over the corner, depending on what else is on that edge.

What giving away a corner looks like

The moment White plays b2, a1 becomes a legal move for Black (a1 → b2 white → c3 black). Black takes the corner, flips b2, and every white disc near the top-left corner becomes a target.

3. In the midgame, fewer discs is better

Many players pick the move that flips the most discs every time. By the midgame they own a large blob of discs, and by the end the blob has been flipped back. Two reasons:

• The more discs you have, the more legal moves your opponent has, and the fewer you have.
• A large blob has many frontier discs, discs next to empty squares, and each one is something your opponent can outflank.

The right habit is to flip as little as necessary in the midgame and save the big flips for the last dozen moves. Disc count only matters at the very end.

4. Mobility decides the midgame

Mobility is the number of legal moves you have right now. The midgame goal is high mobility for you, low mobility for your opponent. When the only moves left to your opponent are X-squares and C-squares, they will be forced to give you a corner. That is not luck; it is what mobility pressure produces.

• Prefer moves that create no new frontier discs: flip discs that are already surrounded rather than discs on the outside. These are called quiet moves.
• Avoid flips that open new squares for your opponent.
• Before each move, count: after this, how many legal moves does my opponent have? Moves that lower that number are usually good.

5. Edges are not automatically safe

Edge discs are harder to flip than central ones, but not impossible. A gap in a row of edge discs is a way in: your opponent can play into the gap and flip the whole row. Before taking an edge, check whether the empty squares on that edge give your opponent a way to outflank you.

6. Parity in the endgame

Late in the game the empty squares split into separate regions. The basic rule: try to be the player who makes the last move in each region, because the last move cannot be answered.

If a region has an even number of empty squares, the player who moves into it second usually gets the last move; with an odd number it is the reverse. Counting the parity of each region is the main reason strong players win endgames that look even.

7. The strong AI rarely slips in the endgame

In ReversiAI, the Hard, Expert and Master levels finish endgames accurately. Against them the game has to be decided in the midgame, through mobility and corner control, not in the final moves. The per-level details are in How to beat the Reversi AI.