Reversi Online

Full Reversi play in the browser

Reversi begins with four discs in the center of an eight-by-eight board. Black moves first. A move is legal only when the new disc brackets one or more opposing discs between the new disc and another disc of the mover’s color along a horizontal, vertical or diagonal line. Every bracketed disc flips immediately. If one side has no legal move, that side passes; the game ends only when neither side can move. The player with more discs then wins.

The board enforces those rules rather than asking you to remember them. Empty legal squares are highlighted, illegal empty squares cannot be played, and pass situations are handled automatically. This matters for practice because a move that looks attractive but does not bracket an opposing line is not silently accepted. The same legal-move engine drives human play, AI play and every tactic position.

Four browser-local AI levels

Vs Computer offers Easy, Standard, Hard and Expert. Easy intentionally varies among legal moves while still respecting the full rules. Standard uses a short look-ahead. Hard searches deeper. Expert uses the deepest local alpha-beta search in this release with a board evaluation that considers disc count, mobility, corners, edges and frontier exposure. The game does not describe Expert as a perfect Reversi solver or attach a fake online rating to it. It is simply the strongest search level that remains responsive in this local-first product.

You can play Black and move first or choose White and let the computer open. Ordinary positions autosave in local browser storage, including the board, side to move and Undo history. No account, remote match server, paid API or cloud database is required.

Why mobility matters more than an early disc lead

Beginners often try to flip the largest number of discs on every turn. That can be a trap. A large early capture may expose many frontier discs and give the opponent several replies. Reversi strategy often values mobility—the number and quality of legal moves—more than the current material count. A smaller move that restricts the opponent can be more powerful than a flashy flip.

Corners are especially valuable because a corner disc can never be flipped. Squares next to an empty corner can therefore be dangerous if they allow the opponent to take that corner. The position coach calls attention to available corners, current mobility and late-game counting rather than pretending a single simple rule solves every position.

120 exact-solved late-game tactics

The tactic bank contains forty Easy, forty Standard and forty Hard positions generated from legal Reversi playouts. Easy positions have four or five empty squares, Standard has six or seven, and Hard has eight or nine. Every position has multiple legal moves. The release generator then solves the game all the way to the final board from every candidate move and keeps only positions with one unique best move.

This is different from labeling a move “best” because a heuristic likes a corner or because it flips the most discs immediately. The tactic answer is verified by exact minimax through every remaining legal sequence, including forced passes. The trainer can therefore report the final perfect-play disc margin of the best move and the gap to the next-best alternative. That makes the exercise a concrete endgame-counting lesson rather than a vague strategy quiz.

Easy, Standard and Hard are calculation depth, not arbitrary labels

Easy leaves only four or five empty squares, so you can often count the remaining move order directly. Standard extends that calculation to six or seven empties, where pass timing and parity become more important. Hard uses eight or nine empties and usually offers more legal choices. The underlying rule is the same at every level: only a position with one exact best move is accepted into the bank.

Failed Review records real misses

If you choose a legal but non-optimal move in Tactics, the board stays on the original position. The miss is stored locally and you can calculate again immediately. A later correct retry records the solve without retroactively granting first-try credit. Failed Review draws from tactics actually missed in this browser rather than inventing a personalized weakness score.

Hint and Undo are study tools

During a full game, Hint points to a move found by a deeper local search and marks the current run Assisted. Undo restores a previous position and also marks the run Assisted. You can still finish the game, but assisted wins remain separate from clean unaided wins and clean best margins. Tactics intentionally hide Hint and Undo because the exercise is to calculate one exact move from a fixed position.

Pass & Play on the same device

Pass & Play uses the same rules for two people sharing the screen. The board automatically changes the side to move, detects passes, and finishes only when both colors have no legal moves. This mode is useful when you want a physical-board style game without an account or online matchmaking layer.

Daily Reversi is separate from Today’s 6

The Daily Reversi Tactic chooses one exact-solved endgame position for the calendar date. Everyone on that date receives the same board and unique best move. The specialist keeps a separate local history and streak and never enters the platform’s existing Today’s 6 rotation, so solving it cannot create a seventh Daily Score slot.

A practical way to improve

Play full games to learn the flow, but use endgame tactics when you want measurable calculation practice. Start by counting legal moves and checking corners. With ten or fewer empty squares, stop judging moves only by immediate flips and begin tracing the move order to the end. When a tactic surprises you, replay it from Failed Review and compare the exact final margin of the correct move with the alternative you first chose.