What is Slitherlink?
Slitherlink is a loop logic puzzle played on a grid of dots and numbered squares. Your goal is to draw one single continuous loop along the dotted grid lines, with no branches, crossings or loose ends.
Each number tells you exactly how many of that square's four sides are part of the loop. A 0 square has no loop edges around it, a 1 square has one edge, a 2 square has two edges and a 3 square has three edges. This free online Slitherlink game gives you several grid sizes, easy, medium and hard puzzles, and a bright friendly board designed for quick play on desktop or mobile.
- Draw one closed loop along the grid edges.
- The loop may not cross, branch or stop halfway.
- Every numbered square must have the exact number of loop sides shown.
- Empty squares can have any legal number of loop sides.
- Every playable puzzle on this page has been checked for one unique solution.
How to play Slitherlink online
Click or tap an edge between two dots to draw a line segment. Click the same edge again to remove it. Keep adding segments until all the chosen edges connect into one clean loop.
Use Check when you want feedback without revealing the answer. Hint adds one correct line from the unique solution, while Solution shows the full loop if you want to study the pattern.
- Start with 0 clues, because all four surrounding edges are excluded.
- Look at 3 clues next, especially when they touch a border or another 3.
- Remember that every dot used by the loop must have exactly two lines.
- Avoid closing a small loop before the whole puzzle is solved.
- Use the undo and erase controls when a chain starts to feel forced in the wrong direction.
Slitherlink grid sizes and difficulty
Small Slitherlink grids are good for learning how numbers affect nearby edges. Larger grids create longer chains where one excluded edge can decide several later moves.
Easy puzzles include more visible clues and friendlier loop shapes. Medium puzzles leave more space for deduction. Hard Slitherlink puzzles use fewer clues, so you have to combine local number logic with whole-loop strategy.
- 5x5 Slitherlink is a compact starting size.
- 7x7 Slitherlink gives a balanced daily challenge.
- 9x9 Slitherlink offers a larger loop with longer deductions.
- Easy, medium and hard change clue density and solving pressure.
- New puzzle rotates through checked boards for the selected setting.
Slitherlink strategy tips
The best Slitherlink strategy is to combine edge counts with dot logic. A dot cannot have one line ending at it, and it cannot have three or four lines meeting there. It is either unused or passes the loop straight through or around a corner.
Number patterns are powerful. A 0 next to a 3 forces many edges, adjacent 3s often create a shared shape, and clues along the border become stronger because there are fewer ways for the loop to enter and leave.
- Mark impossible edges around 0 clues mentally before drawing.
- Use 3 clues to find forced outside edges and corners.
- At every dot, keep the loop degree at either 0 or 2.
- Do not make a separate closed loop while unsolved clues remain outside it.
- When stuck, scan for a clue that already has almost enough lines.
Why unique Slitherlink puzzles matter
A fair Slitherlink puzzle should have one answer. Multiple solutions make it unclear whether a deduction is actually required, and they can turn a clean logic puzzle into guesswork.
The puzzles in this game are bundled from generated loops and checked with a solver so the visible clues lead to exactly one solution. That makes the Hint, Check and Solution buttons consistent with the rules players expect from a proper Slitherlink puzzle.