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Boards and strategy

Reversi

Place a disc to trap a line of your opponent's discs between two of yours, and they all turn over. Most discs at the end wins. Five levels, and a daily game.

Levels
Beginner, Casual, Club, Strong, Master
Daily
Beat Club
Scored by
Win, draw or loss
Today
Daily puzzle
Setting up the board

Rules

  1. 1.The board has 64 squares. The game starts with four discs in the centre: two black, two white, placed diagonally. Black moves first.
  2. 2.On your turn, place a disc of your colour so that one or more straight lines of your opponent's discs (across, up and down or diagonal) lie between the new disc and another of yours.
  3. 3.Every outflanked disc, in every direction at once, turns over to your colour.
  4. 4.A move must turn over at least one disc. If you have no such move you pass, and your opponent moves again.
  5. 5.The game ends when neither player can move, usually because the board is full. The player with more discs wins; equal numbers is a draw.

How to play

Controls
InputAction
Click or tap a squarePlace a disc there; rings mark the legal squares
Arrow keys, then Enter or SpaceChoose a square and place a disc
PassShown when you have no legal move
Take backUndo your last move and the reply
Flip boardSee the position from the other side
  • Beginner: Grabs discs and gives away corners
  • Casual: Knows corners matter, not much more
  • Club: Plays for mobility and reads the last moves
  • Strong: Deep search, perfect over the last twelve moves
  • Master: Deeper still, perfect over the last fourteen

Strategy

  • Corners can never be turned over. Aim to take them, and avoid giving them away.
  • Stay off the squares diagonally next to an empty corner. A disc there often hands your opponent the corner.
  • Count moves, not discs. Early on, having fewer discs and more choices is usually better than grabbing many discs.
  • Try to leave your opponent with few legal moves, so they are forced into bad squares.
  • Edges are strong only when they cannot be attacked. A lone disc on an edge can be outflanked along it.
  • Near the end, count carefully: with a dozen squares left the strong levels play perfectly.

Questions

What happens when I have no move?
You pass and your opponent moves again. The board shows a Pass button when that happens. If neither player can move, the game ends and the discs are counted.
Why did my opponent's disc turn over in two directions at once?
A single move turns over every outflanked line, in all eight directions, not just one. That is how one move can swing the count by a dozen discs.
How strong are the top levels?
Strong and Master search several moves ahead using corners, mobility and the value of each square, and they play the last twelve or fourteen moves perfectly by counting every possible ending.
How does the daily game work?
Everyone plays the same level and colour each UTC day, and the computer answers the same moves in the same way. Win it to extend your daily streak. Takebacks are off in the daily game.

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