Hard Reversi: a 5-ply computer opponent

Hard Reversi plays a computer that searches five moves ahead and plays the last eight empty squares perfectly when its budget allows. It does not blunder corners, so you need a real plan. No app, no sign-up and no interstitial before play; it works offline and plays from the keyboard, with unlimited undo.

How to play hard Reversi

1. The rules are standard Reversi: trap a straight line of the opponent’s discs to flip them.
2. You play dark and move first unless you choose light in settings.
3. The computer searches five moves ahead before replying, usually in a few milliseconds.
4. With 8 or fewer empty squares it counts the exact final result.
5. Most discs at the end wins; equal counts are a draw, which ends the game without a winner.

How to beat hard Reversi

Hard will not walk into simple corner traps; it sees them. You beat it by squeezing its mobility over many moves and by planning further than five moves.

Starve it of moves

Its evaluation counts mobility, so it tries to keep its own options open. Keep your discs in the centre, avoid building walls of your colour along the frontier, and play quiet moves that do not create new targets. When it runs short of good squares, it has to concede an edge or a corner.

Think about parity

Towards the end the board splits into small empty regions. Try to make the last move in each region, especially the odd-sized ones. Forcing a pass gives you two moves in a row, often worth a corner.

Decide before the last eight squares

Once eight or fewer squares are empty, Hard counts the rest of the game exactly. Your advantage has to be built before that point; aim to reach it with more safe discs, a corner or two, and the move.

Replay and learn

The computer is deterministic: the same puzzle code and the same moves give the same game. Undo back to a turning point and try a different move to see how its reply changes. The hint looks three moves ahead, so against Hard it is a check, not a guide.

Hard Reversi stats and hints

Hard keeps its own count of games played and won in your browser; a draw counts as played but not won. There is no timer. Undo takes back your move and the reply, without limit. The first two hints in each game are free; when ads are switched on later, further hints offer a short ad or a 30-second wait.

Plays anywhere, no app, no account

Hard replies within about a tenth of a second on a laptop and a little longer on a phone, and every square can be played from the keyboard. Tidy Puzzles runs entirely in your browser: there is no app to install, no account to create and no interstitial before you can play. After the first visit the game also works offline, because each puzzle is generated on your device from a seed. Every board can be played with the keyboard alone, on a phone or a desktop, and your stats and unfinished puzzles stay in this browser rather than on a server.