Openness and quiet moves

Two similar moves can give your opponent very different options, depending on which discs they flip. Openness puts a number on it.

What openness is

For each disc a move flips, count the empty squares around it, and add them up (each empty square counted once). This is the move's openness. Flipped discs next to many empty squares are easy for your opponent to outflank. Lower openness gives your opponent fewer new moves.

Quiet moves

A move that flips only inner discs surrounded by other discs is a quiet move, typically with openness 0 or 1. Moves that flip many discs tend to flip outer ones too and have high openness.

Checking in a game

1. Look at how many of the discs you would flip touch empty squares.
2. When unsure, prefer moves that flip few, inner discs.
3. A low-openness move that gives a corner is still bad. Compare corners and mobility as well.

Endgame puzzles on this theme

• No. 1● Black · 10 empty
• No. 2○ White · 11 empty
• No. 3● Black · 12 empty
• No. 4● Black · 12 empty
• No. 5○ White · 13 empty
• No. 7● Black · 14 empty
• No. 8● Black · 14 empty
• No. 12○ White · 11 empty
• No. 14○ White · 13 empty
• No. 18● Black · 12 empty
• No. 20● Black · 14 empty
• No. 21● Black · 10 empty
• No. 22○ White · 11 empty
• No. 25● Black · 14 empty
• No. 26● Black · 10 empty
• No. 27○ White · 11 empty
• No. 29○ White · 13 empty
• No. 30● Black · 14 empty
• No. 42○ White · 11 empty
• No. 43● Black · 12 empty
• No. 44○ White · 13 empty
• No. 45● Black · 14 empty
• No. 46● Black · 10 empty
• No. 51● Black · 10 empty
• No. 52○ White · 11 empty
• No. 53● Black · 12 empty
• No. 55● Black · 14 empty
• No. 61● Black · 10 empty
• No. 62○ White · 11 empty
• No. 63● Black · 12 empty
• No. 64○ White · 13 empty
• No. 65● Black · 14 empty

Play the dojo and get every move graded →

Reversi strategy

• Corners, X-squares and C-squares
• Mobility: leave fewer moves
• Parity
• How to read the endgame