How to play Dots and Boxes

Dots and Boxes is the pencil-and-paper game of lines and squares. The board is a grid of dots. The two players take turns drawing a single line between two neighbouring dots, and whoever draws the fourth side of a box claims it and must draw another line. When every line has been drawn, the player with more boxes wins.

It looks like a children's game, and for the first few minutes it plays like one: nobody wants to draw the third side of a box, because that hands it to the opponent. But sooner or later every safe line is gone, the board has turned into long corridors of boxes called chains, and someone has to open one. From that moment the game is decided by counting, and a player who understands chains can win almost every box on the board while appearing to give some away.

How to play on skill.games

In the settings popup choose a difficulty (Easy, Normal, Hard or Crazy), a board size and who draws the first line, then press PLAY. Your lines are blue, the computer's are red.

• Drawing a line: tap between two dots. You can also press and slide: the free line nearest your finger lights up and follows it, and lifting your finger draws that line.
• Taking a box: when your line closes a box, the box fills with your colour and your initial, and you draw again (the status line says BOX! YOUR TURN AGAIN). Keep going until you draw a line that closes nothing.
• The latest line shines briefly, so you can always see what the computer just drew. The computer also takes its boxes one line at a time, so you can follow every capture.
• Score line: the top of the screen counts the boxes each side owns and shows whose turn it is.

The menu button in the top-left corner pauses the game and lets you resume, start a new game or switch the sound on or off. The game is saved after every line, so an unfinished game can be picked up later with CONTINUE.

At the end the results screen shows the final box count, the board size and the number of lines drawn, together with your statistics for that board and difficulty: wins, losses, draws, win rate, current streak and best streak.

Rules

• The board is a rectangle of dots; on skill.games it has 3 x 3, 4 x 4 or 5 x 5 boxes (16, 25 or 36 dots).
• Players take turns. A turn is one line joining two dots that are next to each other, across or down. Diagonal lines are not allowed, and a line can only be drawn once.
• If your line completes the fourth side of one box (or of two boxes at once), you own those boxes and you must draw another line. A turn ends with the first line that completes nothing, or when the board is full.
• Drawing is compulsory: you cannot pass, even if every line left gives something away.
• When all lines are drawn, the player with more boxes wins. On the 4 x 4 board, with sixteen boxes, the game can end in a tie.
• Who draws the first line is chosen in the settings: you or the computer.

Strategy tips

• Don't draw the third side. Early on, a line that gives a box a third side lets your opponent take it for free. Draw lines that leave every box with at most two sides.
• Watch the chains form. As safe lines run out, the boxes link up into chains (corridors open at both ends) and loops (closed rings). Once nothing safe is left, every move opens one of them.
• Open the smallest thing first. When you must give something away, give the shortest chain. A chain of two is best opened in its middle, so your opponent can't play the trick below.
• The double-cross. When your opponent opens a long chain, you don't have to take all of it. Take every box except the last two, then draw the line at the far end, leaving those two boxes as a pair. Your opponent takes the pair with one line and then has to open the next chain for you. You sacrifice two boxes to keep control; in a loop the price is four.
• Keep control when the chains are long. The double-cross pays when the chains still to come are worth more than what you give back. With one chain left, or only short ones, just take everything.
• The long chain rule. Whoever ends up forced to open the first long chain usually loses. Experts count dots and chains early to steer that parity: on a board with an odd number of dots (the 4 x 4 board has 25) the first player wants an odd number of long chains, on an even number of dots an even number. Sacrificing a box or two in the middle game to change the count is a strong, advanced idea.

Difficulty levels

• Easy: sometimes misses a box it could take and sometimes draws a third side when it didn't need to. It never plans for the chains.
• Normal: takes every box offered, never gives one away while a safe line exists, and when it must give something it gives as little as possible. It always takes a whole chain, though, so it can be beaten by the double-cross.
• Hard: plays the endgame like an expert: it opens the right chain at the right time, and it double-crosses whenever keeping control is worth it. Its safe moves earlier on are chosen at random.
• Crazy: everything Hard does, plus it plans the middle game for the long chain rule, playing out the rest of the safe moves in its head to see who will have to open the first long chain. On the last 19 lines it calculates the game exactly and never makes a mistake.

Modes

• Board: 3 x 3 (nine boxes, a quick game), 4 x 4 (sixteen boxes, the classic size; a tie is possible) or 5 x 5 (twenty-five boxes, where the chain battle takes longest). Each board keeps its own statistics.
• First line: you or the computer. On a given board one side has a theoretical edge, but at human level the chains decide far more than who started.