Most games of Dots & Boxes aren't won by the player who closes the most boxes early. They're won by the player who decides who has to open the first long chain. Here's how that works, and how to use it in Classic mode in Dots & Boxes Collection.
Don't draw the third side
The first habit is simple: never draw the third side of a box unless you have to. A box with three sides is a free box for your opponent, and closing it also gives them another turn.
In the game, these moves are easy to spot. Dashed risky lines mark every move that would hand a box away, so early on you can play only solid lines and know you're safe.
Why the board turns into chains
Safe moves run out. When they do, the board has settled into strips of boxes that are each missing two sides. These strips are chains.
Once only chains are left, every move opens one of them. Whoever opens a chain gives its boxes to the other player, who can then keep going while each box they close earns another turn.
Take all but two
Here's the move that separates beginners from strong players. When your opponent opens a long chain, three boxes or more, don't take every box. Take all of them except the last two, then draw the line at the far end that leaves those two as a pair.
Your opponent closes the pair, which earns them one extra turn. With no safe moves left, they must use it to open the next chain for you. Players call this the double-cross. Giving up two boxes to keep control is almost always worth it when more chains are still waiting.
On the very last chain of the game, keeping control no longer matters, so take everything.
The real fight: who opens the first long chain
Once both players know the double-cross, the game becomes a battle for control. The player forced to open the first long chain usually loses, because their opponent can double-cross every chain after that.
So strong players think ahead in the middle of the game. Sometimes they make small sacrifices, giving away one or two boxes on purpose, to change whose turn it will be when the safe moves run out. Counting the chains forming on the board, and how long each one is, is the skill to build. Expert players have studied this deeply. The Dots and Boxes article on Wikipedia is a good starting point, with references to Elwyn Berlekamp's book on the game.
How to practice
- Start on Easy and play only solid lines. Notice the moment the board runs out of safe moves.
- Use Hint when you reach the chain phase, and think about why it picks the chain it does. Giving away a short chain costs less than giving away a long one.
- Try the double-cross on Standard. Standard plays a little sharper each time you win and eases off when you lose, so it keeps pace as you improve.
- Test yourself on Hard once taking all but two feels natural.
A note on the other modes
This guide is about Classic. The other three modes change the goal or the rules, so the chain logic plays out differently. In Reverse the fewest boxes win, so you no longer want the chains for yourself. In Takeover, closing a box can flip a trapped row of your rival's boxes. In Trapline, every line starts where the last one ended, which changes which moves are open at all. Each one is worth learning on its own terms.
Dots & Boxes Collection is free on Google Play and plays fully offline. You'll find more about it on its page.