How to Play Slitherlink Puzzles

Slitherlink Rules

Slitherlink is played on a lattice of dots. Between the dots lie cells, and some cells contain a number from 0 to 3 (a 4 is possible but rare). Your task is to draw edges between horizontally or vertically adjacent dots so that the drawn edges form one single closed loop, and every number equals the count of drawn edges on that cell’s four-sided boundary.

A 0 means no edge of that cell is on the loop, so all four are banned. A 3 means three of the four edges are drawn. Cells without a number impose no constraint of their own, but they still carry loop segments. The loop may never cross itself, never branch, and never split into two loops: at every dot, exactly 0 or 2 edges meet.

Solving alternates between two viewpoints: local counting (what each number still needs) and path topology (where loose ends can still travel). Numbers force edges and bans; bans force paths; paths close the loop. Every puzzle on this site is machine-verified to be completable by this kind of step-by-step logic, with no guessing at any point.

Step-by-Step: Solving a Slitherlink

1. Cross out every edge touching a 0. These bans are certain and immediately constrain the neighboring clues.
2. Handle the borders. A 3 at a corner or along the border forces specific edges; two 3s beside each other force a whole corridor of lines.
3. Count each number to completion. When a clue’s count is reached, ban its remaining edges; when it needs every edge it has left, draw them all.
4. Follow the path ends. A dot with exactly one line must gain exactly one more; if only one free edge remains there, draw it, and never let a path close into a loop while clues are still unsatisfied.
5. Repeat until the last two loose ends meet. The loop closes, every number is satisfied, and the grid is solved.

Slitherlink Tips & Techniques

• Zeros are free edges crossed out. Every edge touching a 0 is definitively not part of the loop; those bans feed every other deduction around them.
• A 3 corner pins three edges at once. Any 3 in a grid corner, or against the border, forces its two border edges plus one more; look for these before anything else.
• Track the path ends. Every loose end of a partial path must eventually connect to exactly one more edge; when a dot has one line and only one free edge left, that edge is forced.
• Never close a loop early. If drawing an edge would seal your path into a loop while other clues remain unsatisfied, that edge is wrong; crossing it out is often the strongest move on the board.
• Add numbers as you go. Keep a running count per clue cell: once a cell’s number is satisfied, all its remaining edges are banned, exactly like a zero.

Frequently Asked Questions