Strategy
Slitherlink Strategy & Solving Tips
A practical strategy guide for Slitherlink: start with 0s and 3s, use the dot rule, mark X on ruled-out edges, avoid closing the loop early, and reason about inside and outside.
Play SlitherlinkThe core idea
Certain moves first, guesses never
Almost every strong Slitherlink habit comes down to two ideas: make every certain deduction the board offers before you think about anything harder, and record what you have ruled out with X marks so nothing is ever forgotten. Every puzzle here has one solution, so a guess is never required — only the next deduction.
- 01
Start with the 0s
A 0 rules out all four of its sides, so put an X on each. Then look at the cells next to it: any shared side is already an X, which often forces a neighbouring 1, 2, or 3 to use its other sides.
- 02
A 3 beside a 0 is a gift
The side they share is ruled out by the 0, so the 3 must use its other three sides. A 3 in a grid corner works the same way: both of its outer sides are lines, because the board edge leaves no other option for two of the three.
- 03
Adjacent 3s
Two 3s side by side always share a line between them, and the far outer side of each 3 is also a line. Three parallel lines, all certain. It is one of the most useful patterns on the board.
- 04
Corner 1s and 2s
In a grid corner, a 1 cannot use both outer sides (that would be two lines), and a line there would create a dead end at the corner dot, so both outer sides are X. Corners are a good place to check for forced dots.
- 05
Use the dot rule constantly
Every dot has zero or two lines. A dot with two lines gets X marks on every other gap. A dot with one line and only one open gap must continue. A dot with no lines and only one open gap must stay empty. Scanning dots is how you find moves when the numbers run out.
- 06
Never close a small loop
If joining two ends of a path would close a loop while other numbers are still unsatisfied or other lines exist elsewhere, that join is an X. Before drawing the last edge of a path, ask whether it closes the whole loop or just part of it.
- 07
Think inside and outside
The loop splits the board into inside cells and outside cells, and two neighbouring cells are on opposite sides only if a line separates them. A 3 tends to be surrounded by cells of one type, a 1 or 2 by mixed cells — use that to chase forced regions when the local rules are exhausted.
- 08
Mark X liberally, undo freely
X marks cost nothing and make later deductions visible. Undo and redo are unlimited, so you can test an edge, see whether a clue or dot breaks, and take it back. The Check button flags lines that are not in the solution if you want to confirm a hunch.
By grid size
How the approach shifts with size
The habits above apply to every size. What changes is how far ahead you have to follow a path — see the grid sizes section of the guide.
On 5×5
Most puzzles fall to 0s, 3s, and the dot rule alone. Use it to build habits: scan for 0s, then for 3s, then for dots with two lines, and repeat.
On 7×7
Expect to track two or three separate path fragments and join them. Place X marks as you go so you can see which ends still have only one way to continue.
On 10×10
Long loops with sparse numbers. Work one region at a time, and use inside / outside reasoning when local patterns dry up. Some places may need you to follow a hypothetical path several steps.
Ready to put it into practice? Read the full how-to-play guide or jump straight in.
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