Slitherlink

A loop-drawing logic puzzle. Connect the dots along the grid lines to form one single closed loop that never crosses or branches. Every number tells you exactly how many of the four edges around its cell the loop must use, and there is always exactly one solution reached by pure deduction — no guessing.

How to play

The board is a grid of dots. Your job is to join neighbouring dots with horizontal and vertical segments so that the segments you draw form exactly one closed loop — a single unbroken ring that never crosses itself and never branches off in a third direction.

The numbers are your clues. A number sits inside a cell and counts how many of that cell's four edges the loop runs along: a 0 means the loop touches none of its four sides, a 2 means exactly two of them, a 3 means three. Cells with no number can use any count of edges.

Tap the gap between two adjacent dots to place an edge there. Tapping the same gap again turns it into a small ✕, which marks an edge you are sure the loop does not use — handy for keeping track — and a third tap clears it back to blank. A clue turns grey once the loop uses exactly its number of sides, and red if you have drawn too many, so you can spot mistakes early.

When your lines make one single closed loop that satisfies every number, the puzzle is solved. Each board has exactly one solution and can always be cracked by logic alone. Your finishing time is your score, so faster is better.

Tips & strategy

Start with the extremes. A 0 means none of that cell's four sides are used, so you can immediately mark all four with ✕ — and those ✕ marks often force neighbouring edges. A 3 next to another 3, or a clue tucked in a corner, also pins down edges right away. Clearing the forced cells first untangles everything else.

Lean on the ✕ marks as much as the lines. Knowing for certain where the loop does not go is just as powerful as knowing where it does, because every dot must end up with either zero or exactly two lines. If a dot already has two lines, every other edge at that dot must be ✕.

Watch the dots, not only the numbers. The loop can never dead-end: a single line arriving at a dot must always leave it, so a dot with one line and two ✕ marks forces the fourth edge to be a line. Chasing these forced exits around the grid is how most of the solving actually happens.

Avoid making little closed loops too early. Because the finished figure must be one single loop, any short ring you accidentally close off can never be part of the answer — if a line would seal a small loop while edges elsewhere are still unused, that line has to be wrong.