Slitherlink techniques

Slitherlink is built on a handful of patterns that repeat across every puzzle. Learn to spot them and the loop starts drawing itself. Crosses matter as much as lines, so mark them as you go.

In each picture, the cells the technique decides are outlined in blue.

1. Zero means no lines

   A 0 uses none of its sides. Cross out all four before anything else. Each cross tells the dots next to it which ways the loop can’t go.

2. A 3 beside a 0

   The side a 3 shares with a 0 is crossed, so the 3 must use its other three sides.

3. Two 3s side by side

   Two 3s next to each other always use the side between them and both far sides. The lines that would carry the middle line on past them are crossed.

4. Numbers in corners

   The corner dot of the grid has only two sides, so the loop uses both or neither. A 3 in a corner needs both. A 1 in a corner can’t use either.

5. Two lines at every dot, or none

   The loop passes straight through dots, so each dot has exactly two lines or none at all. A line that reaches a dot with only one way left to go must take it.

6. Don’t close a loop too soon

   There’s only one loop. A line that would close a small loop while other lines are still waiting to be joined must be crossed out.

When you’re stuck, pick an undecided gap next to a busy area and imagine drawing a line there. If that forces a dot to take three lines, or a number to go over, the gap gets a cross.