Slitherlink — Draw the Loop

Slitherlink is a loop-drawing puzzle published by the Japanese puzzle company Nikoli since 1989. The name in Japanese is スリザーリンク. You might also see it called “Loop the Loop” in British puzzle magazines, “Fences” in some puzzle apps, or simply “loop puzzle.” The puzzle is the same under every name.

You get a grid of dots forming a lattice. Some cells between the dots contain a number from 0 to 3. Your job is to draw line segments along the edges between dots so that (1) each numbered cell has exactly that many line segments on its edges, and (2) all lines connect into a single closed loop with no branches or loose ends.

The puzzle gained international popularity alongside Sudoku in the mid-2000s. It shows up regularly in puzzle competitions, particularly at the World Puzzle Championship. Solvers in Japan, the US, Germany, India, and across Europe play it both in print and online. We have 1,500 puzzles across five difficulty levels, from 5×5 grids for beginners to 14×14 grids certified solvable by logic alone.

Two constraints, nothing else. First: each number clue tells you how many of that cell's four edges (top, right, bottom, left) are part of the loop. A 0 means none. A 3 means three out of four. Cells without a number can have any count. Second: every line segment must connect into a single closed loop. No branches, no dead ends, no separate loops.

Click or tap an edge to cycle it: empty → line → excluded → empty. Lines are drawn bold. Excluded edges get an × mark so you can track what you've ruled out. The clue numbers change colour as you work — grey when untouched, copper when partially filled, green when satisfied, red when over-constrained. The hint system walks you through the next logical step if you get stuck.

For the full rules with worked examples and common patterns, see the rules page.