Dots and Boxes

The basics

Draw one line per turn: tap a gap between two neighbouring dots and the line appears. Lines run only along the grid, never diagonally, and each one can be drawn once. When your line closes the fourth side of a square, that box turns your colour and your score goes up, and you draw again; closing two boxes with one line is possible where two squares share their missing side. When you cannot claim anything, play a line that leaves the computer as little as possible: a square with three sides is a gift, and two or three of them in a row is a chain the computer will take in one run. The game ends when all boxes are claimed. Easy plays loosely and sometimes hands back a box; Medium takes every free box and otherwise gives away the smallest opening; Hard plays the rest of the board out for each candidate line and keeps the one with the best final margin. None of the three plays the double-cross, so a chain you open is usually taken to the end. Hint marks one line from the Hard policy and counts itself for the current game; it never changes the score. Your wins, losses and draws per board size and level, and the sound setting, stay in this browser only. There is no undo — Restart starts the same board size and level again. Add ?size=6&level=hard&seed=7 to the URL to pin the board, the level and the computer's tie-breaks.

Objective:

Claim more boxes than the computer. You and the computer take turns drawing one line between two neighbouring dots. A square whose fourth side you draw is yours, your count goes up and you draw again, so one good line can start a run. The game ends when every box is claimed: 16 on the 4×4 board, 25 on 5×5 and 36 on 6×6. More boxes wins; 4×4 and 6×6 can end level because their box count is even, while 5×5 cannot. There is no clock and no move limit — boxes are the only score.

Controls:

Tap or click a gap between two neighbouring dots to draw that line; on a touch screen you can also press and drag along the board — the line under your finger is previewed and the one you release on is drawn. Mouse and touch work the same way. Buttons: 4×4 / 5×5 / 6×6 pick the board, Easy / Medium / Hard pick the opponent, Hint marks a suggested line, Restart starts the same board again, Rules opens the rules sheet and Sound toggles the synthesised blips. Every chip and button is at least 22 px tall on the 348x261 phone stage and the whole shell fits there without scrolling; on the 894x670 desktop stage the board is at least 560 px square.