How to Solve Slitherlink: Rules, Tips and Strategies for Beginners
Slitherlink is the loop logic puzzle by Nikoli (the Sudoku company): draw a single closed loop along the grid lines so that every numbered cell has exactly that many of its four sides used by the loop. Cells without numbers impose no rule at all. It looks minimal — just dots, lines and a few digits — but the loop builds itself from a handful of simple rules. Here's how it works and how to draw your first one confidently.
The rules in one minute
Draw a single closed loop along the grid lines — it never crosses or branches. Every numbered cell must have exactly that many of its four sides used by the loop. Cells without a number impose no rule at all. The loop may touch itself at corners, but it must be one continuous, unbroken ring. Every slitherlink puzzle has exactly one solution.
How to read the clues
Each number sits inside a cell and says exactly how many of that cell's four sides your loop must use. A 0 means none of its sides are drawn; a 1 means exactly one; a 2 means two; a 3 means three. Blank cells are free — the loop may use any number of their sides, including none. On our slitherlink generator you click grid lines to draw them, click again to cross them out as notes, and a third time to clear. If you just want the plain rules without the strategies, our rules page has them all in one place.
1. The 0 rule: cross out all four sides
Whenever you see a 0, none of its four sides can be part of the loop — cross them all out immediately. Every crossed-out line is information: it tells the neighbouring cells what they can't use, and it can force other lines. The 0s are your first footholds, and on easy puzzles they appear on purpose to get you started.
2. The 3 rule: draw three, cross out the fourth
A 3 is nearly as strong. Since exactly three of its four sides are used, you can draw three of them right away — but which three? The moment any one side of a 3-cell is crossed out, the other three are forced on; the moment any one side is drawn, the remaining side is forced off. Keep an eye on the cells next to a 3 and the pattern resolves itself quickly.
3. Corners and edges are the most constrained
A corner cell has only two sides in play, so its number is very strict: a corner 2 uses both its sides, a corner 1 uses exactly one, a corner 0 uses none. Edge cells have only three sides. These constrained cells give you definite lines and definite crossings early on, and they anchor the loop while the interior slowly fills in.
4. Remember: there is only one loop
The biggest beginner mistake is closing a small loop and stopping. The puzzle has exactly one ring, so any closed circle that isn't the whole solution is a wrong turn — the loop must keep growing until it has threaded through every constraint. If you're about to close a loop early, check whether every numbered cell is already satisfied; if not, that closure is wrong.
5. Mark the lines that can't be used
Crossed-out lines are just as valuable as drawn ones. When a cell already has its full count of sides used, cross out its remaining sides; when two drawn lines would force a crossing or a branch, cross one of them out. On paper, keep two marks distinct — a heavy line for "in the loop" and a small × for "definitely out". Most slitherlink techniques produce both kinds of information at once.
6. Avoid the classic mistakes
Three errors trip up beginners. First, crossing or branching the loop — at every vertex the loop either passes straight through, turns, or doesn't visit at all; it never splits. Second, forgetting that blank cells still matter when they share a vertex with numbered ones — a line through a blank constrains the loop's path. Third, closing the loop early (see rule 4). Check your finished loop against every number, and if you're stuck, the answer key shows the one true ring.
Practice with a printable slitherlink
Slitherlink is all about pattern recognition, and the patterns come with practice. Generate a fresh puzzle in seconds on the slitherlink generator — pick a difficulty and grid size, then print the blank grid or draw on screen. Start on 4×4 easy, where the 0s and 3s do most of the work, then move to 5×5 and 6×6 as the loop grows longer and the logic deepens. If you enjoy drawing-to-solve puzzles, nonograms are a natural companion — and for pure logic in a grid, our kakuro guide has you covered.