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Spark Boxes strategy: how to beat the bot

Spark Boxes is dots and boxes. You take turns drawing a line between two neighbouring dots. If your line completes a shape, it is yours and you must go again. The player with the most shapes at the end wins. The game looks like luck for the first few minutes and turns out to be about one idea, control: who is forced to open the first long chain near the end.

The basic rule: never draw the second-to-last line

A shape with three sides drawn can be completed by anyone, including your opponent. So the single most important habit is not to draw the line that gives a shape its third side (on a square board), or its second-to-last side in general. Doing that hands the shape to your opponent, who takes it and then moves again.

Phase one: safe moves

The early game is a countdown. Both players draw lines that do not give anything away, and the supply of safe lines shrinks. Neither player can avoid it. The player who runs out of safe moves has to give something away first. Nearly all the skill is in controlling who that will be.

Chains and loops

When the safe moves run out, the board is split into regions of connected shapes. A chain is a row of shapes with open ends, and a loop is a chain joined in a circle. If you open a chain, your opponent can take every shape in it. The twist is the double-cross: instead of taking the last two shapes in a chain, a player who wants to keep control can decline them, leaving two shapes for the opponent, and be the one who does not have to open the next chain.

• Short chains (one or two shapes) are the ones to open first, because they cost little.
• Long chains (three or more) are valuable. Open one and your opponent takes most of it.
• Loops cost more to give away than chains, because declining at the end leaves four shapes behind, not two.

The counting rule on square boards

For an ordinary square board there is a well-known rule of thumb: the first player wants the number of dots plus the number of long chains to be even, and the second player wants it to be odd. In practice, count the dots on the board and the long chains that seem to be forming, and steer the board toward the count you need by merging chains or splitting them. The rule is a guide and not a guarantee, and the triangle and octagon boards have different shapes and different counting, so use it mainly on squares.

Sacrifices

Giving up one or two shapes early can win you control. If handing over a small chain means your opponent has to open the first long one, you will gain more than you gave. Likewise, when your opponent offers you a long chain you can usually take all but the last two shapes and decline the rest, keeping control while still scoring.

Playing the bot

The bot comes in levels from easy to impossible. Against the lower levels, simply avoiding giving shapes away is usually enough. Against the higher levels the chain endgame is decisive, so the opening matters: keep the safe-line count in your mind, and do not be the player who runs out first. If you are losing the count, try to create a large number of short chains or to merge two long chains into one.

To zoom the board, pinch with two fingers; to draw a line, drag from one dot to the next. Pinching never draws a line by accident.