Slitherlink

Slitherlink is a logic puzzle played on a square grid. Some cells contain a digit from 0 to 3, and the objective is to draw a single continuous loop along the grid lines that border the cells. The loop must not pass through cell interiors or cross itself, and it may not form branches or separate subloops.

Each digit indicates how many of the four edges of that cell are used by the loop. For example, a 0 means none of the cell’s edges are part of the loop, while a 3 means three of the four edges are used. A 4 does not appear in standard puzzles. The loop travels along the grid lines, so the status of shared edges is constrained by the digits in adjacent cells.

Solving Slitherlink relies on logical deduction. Beginners often start with cells showing 0 or 3, which force certain edges to be marked. More advanced techniques examine how edges around neighboring digits interact, use chains of possibilities, and exploit consistency across the grid. Although some puzzles can be solved purely by deduction, others may require speculative trial and backtracking; well-designed puzzles typically have a unique solution.

Variants and naming: in English-language puzzle literature, the puzzle is commonly called Slitherlink, and it is also known as Loopy or Loop the Loop in certain books and software. It belongs to the family of Nikoli loop puzzles and is widely published in puzzle books, magazines, and online collections.

Grid size and gameplay: puzzles range from small grids to very large ones, with difficulty varying accordingly. The objective remains the same: produce one non-self-intersecting loop that satisfies all numerical clues.