How to Win at Dots & Boxes: Chains and Double-Cross
Dots & Boxes looks simple, but strong players win it in the endgame, where whole chains of boxes change hands. Grabbing every box you are offered is how beginners lose to the Hard computer. This guide explains the safe opening, the long chain rule that decides who gets the big chains, and the double-cross that keeps you in control.
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Never draw the third side early
A box with three sides drawn is a gift: your opponent takes it and moves again. In the opening, draw only lines that leave every box with two sides or fewer. The yellow ! on the line preview warns you when a line gives a box away. Eventually the safe lines run out, and whoever must move first then has to open something.
When you must give, give the least
Once no safe line is left, hand over the smallest region possible: a single box or a chain of two rather than a long chain. When you give away a chain of two, draw the line in the middle of the pair, not at its end. That leaves two separate boxes, so your opponent cannot answer with a double-cross.
Learn the long chain rule
A long chain is a row of three or more boxes that can all be taken one after another. In the endgame, the player who is forced to open the first long chain usually loses. On every board here, 4×4, 6×6 and 8×8 boxes, the player who draws the first line wants an odd number of long chains, and the second player wants an even number. Loops do not count.
Shape the middle game with that in mind: join two short chains into a long one, or cut a long chain in two, to set the count in your favour. Against the computer the first player is chosen at random, so check who started.
Master the double-cross
When your opponent opens a long chain and you are in control, take every box except the last two, then draw the line at the far end that leaves those two boxes as one pair. Your opponent takes the pair but then has to open the next chain for you. In a loop, leave the last four boxes. On the final chain there is nothing left to control, so take everything.
Count before you sacrifice
A double-cross costs two boxes, or four in a loop, every time. Before you give them up, add up the remaining chains: if keeping control wins you more boxes than it costs, do it; if not, take the whole chain. On the 4×4 board there are 16 boxes, so 9 wins and 8 to 8 is a draw. Practise the chain battle on 6×6 against the Hard computer, then try it against a friend online.
Questions
- Do I play again after closing a box?
- Yes. Every time your line completes one or two boxes, you score them and must draw another line.
- What is a double-cross?
- Declining the last two boxes of a chain by drawing the line that leaves them as a pair. Your opponent takes them but must then open the next chain.
- Why does the Hard computer keep winning the endgame?
- It counts chains and loops and uses double-crosses. Avoid opening long chains, sacrifice small regions first and aim for the long chain count that suits you.
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