How to play

Black moves first, then the players take turns placing one disc of their color. A move must trap one or more of the opponent's discs in a straight line — across, up and down, or diagonally — between the new disc and another disc of your color. Every trapped disc flips over to your color. One move can flip lines in several directions at once.

If you have no legal move, your turn passes. The game ends when neither player can move, usually because the board is full. Whoever has the most discs wins (the fewest in Anti-Othello).

Variants

Standard Othello — 8×8 board starting with two black and two white discs in the middle.

Original Reversi — the 8×8 board starts empty. The first four discs (Black, White, Black, White) must go in the four middle squares and flip nothing. After that, play is normal.

Small Board (6×6) — a shorter, sharper game on a 6×6 board.

Grand Othello (10×10) — a longer game on a 10×10 board.

Anti-Othello — normal board and moves, but the player with the fewest discs at the end wins.

Octagon Board — the three squares at each corner of an 8×8 board are removed, giving an eight-sided board.

Blocked Squares — four squares, in two mirrored pairs, are blocked off at random each game. Nothing can be placed there, and a line of discs stops at a blocked square.

Handicap — Black starts with one to four corner discs already on the board. Traditionally the weaker player takes Black. Black still moves first.

Players and options

Play against the computer at Easy, Medium or Hard, as Black or White, or choose Two Players to share one device. Undo takes back your last move (and the computer's reply) as many times as you like. The legal-move markers show every square where the player to move can play; turn them off on the setup screen if you prefer.

The Oracle

The Oracle is your optional advisor. Tap 🔮 The Oracle and it stays on duty, advising at the start of each of your turns until you close it. In Two Players it advises whoever's turn it is.

It uses minimax: for every move you could make it imagines each reply, each answer to that reply, and so on, assuming both sides play their best, then scores the move by how that ends. It looks as far ahead as it can in about four seconds. Near the end of the game it can see all the way to the last move, so its answers there are exact.

A green tag means that move forces a win: "Win in 3 · by 12" means three of your moves (this one included), finishing 12 discs ahead when both sides play their best (in Anti-Othello, 12 discs fewer). Among winning moves the Oracle ranks the biggest margin first. Grey means best play ends in a draw; red means it loses against best play (ranked by the smallest losing margin); amber is the Oracle's look-ahead score when it can't yet see the end (bigger is better for you). It weighs corner and edge squares, squares next to corners, how many moves each side has, and late in the game the disc count.

The best move is shown on the board: the gold ring is where to place your disc, and the purple glow marks the discs it would flip. Tap another option in the list to see that one instead. The Oracle only advises you; the computer player plays its own way regardless.

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