Dots and Boxes is the game children draw in the margins of school books, and it hides one of the deepest endgames of any simple game. Draw lines, close boxes, and learn when to give boxes away so that you can take the long chains at the end.
Rules
Dots sit in a grid of 3×3 up to 6×6 boxes. Dark starts. A turn is a single line joining two dots that are next to each other, horizontally or vertically.
Finish the fourth side of a box and it becomes yours, and then you must draw once more. A single line may finish two boxes. The turn goes on for as long as each line closes something.
When every box has been claimed, the player with more boxes wins. On boards with an even number of boxes an equal split is a draw.
Strategy
Never hand over a third side. A box with three sides is free for the taking. Early on, both players look for lines that give nothing away, until such lines run out.
Count chains before you move. Once no harmless line is left, the board has broken into chains (corridors of boxes) and loops. The player obliged to open the first long chain is usually the one who loses.
Double-dealing. When you take a chain the opponent opened, you can stop two boxes short and leave them with one line that closes both. They take two boxes, but then they must open the next chain for you. Giving up two boxes to keep control often wins the game.
The long chain rule. On a board with an odd number of dots, the first player wants an odd number of long chains (three boxes or more); the second player wants an even number. Steer the opening so the count comes out your way.
Questions
Do I have to take a box when I can?
No. Taking is allowed but not forced. Declining the last two boxes of a chain is one of the main skills of the game.
What is a loop?
A ring of boxes with no ends. When a loop is opened, the player who takes it can give away the last four boxes instead of two to keep control.
Which board size should I choose?
3×3 is quick and good for learning. 4×4 is the usual game. 5×5 and 6×6 have more chains and longer endgames.
Why did the computer give me boxes?
On the higher levels it does this deliberately: it hands over a few boxes so that you have to open the next long chain for it.
How do I draw a line on a touch screen?
Tap the gap between two dots. The nearest free line is drawn; with a mouse, hovering shows which line you are about to draw.