Slitherlink is also called Fences, Loop the Loop or Loopy. It comes from the Japanese puzzle publisher Nikoli.
The rules
- Draw one closed loop along the dots, with no crossings and no branches.
- The loop goes from dot to dot along the sides of the squares, across or up and down.
- A number tells how many of its square's 4 sides the loop uses.
- A square without a number can use any number of sides.
- The loop can skip dots. It does not have to pass every dot or every square.
- There is only one loop. Every line you draw must be part of it.
So in the end, every dot has 0 or 2 lines. A dot never has just 1 line, and never 3 or 4.
These are the classic Nikoli rules. Quirk uses square boards from 3 by 3 up to 7 by 7 squares, with numbers from 0 to 3.
A worked example
This board has 2 rows of 2 squares, so it has 3 rows of 3 dots.
| Row | Left | Right |
|---|---|---|
| Top | 1 | 1 |
| Bottom | 3 | 3 |
- Look at the bottom left 3. It sits in the corner of the board. The corner dot has only 2 sides: the left edge and the bottom edge.
- The 3 leaves out just one of its sides. If it left out a corner side, the corner dot would have 1 line. That is not allowed, so draw both corner sides.
- Do the same for the bottom right 3. Draw its right side and its bottom side.
- Now look at the dot in the middle of the bottom edge. It already has 2 lines, one from each 3. Cross out the side that goes up from it.
- That crossed side lies between the two 3s. Each 3 now has 2 lines and only its top side left. Draw the top side of both 3s.
- Follow the lines. They make one closed loop around the two bottom squares.
- Check the two 1s. Each one touches the loop only on its bottom side. Both numbers match, so the puzzle is solved.
Beginner techniques
Start at the 0
A 0 means the loop uses none of its sides. Cross out all 4 sides. A 3 next to a 0 must then use its other 3 sides.
Count at every dot
Every dot needs 0 or 2 lines. A dot with 2 lines is done, so cross out its other sides. A dot with 1 line and only 1 open side must go on there.
A dot with no lines and only 1 open side cannot use it. Cross that side out.
Look at the corners
A 3 in a corner of the board always uses both corner sides. A 1 in a corner never uses them, so cross out both.
Full numbers and hungry numbers
When a number has all its lines, cross out its other sides. When a number needs every side it has left, draw them all.
Do not close the loop too soon
There is only one loop. Never close a small loop while other lines are left out of it. Never close it while a number still needs lines. Cross out the side that would close it.
Common mistakes
- Making two loops instead of one.
- Leaving a line with a loose end.
- Letting 3 or 4 lines meet at one dot.
- Forgetting that the corner dot next to a 3 needs 2 lines.
- Thinking the loop must visit every dot. It can skip dots and empty squares.
Questions
Is Slitherlink the same as Fences or Loop the Loop?
Yes. These are names for the same puzzle with the same rules.
Does every puzzle have one solution?
Yes. Each Slitherlink puzzle in Quirk has exactly one loop that fits all the numbers.
What sizes are there?
Quirk boards are square, from 3 by 3 squares up to 7 by 7 squares. Harder levels need trickier steps, not just bigger boards.
Do I have to cross out every side the loop does not use?
No. Crosses are only there to help you think. The puzzle is solved as soon as your lines form the right loop.
Can a number be 4?
Not in Quirk. A 4 would make the loop just one square. Quirk numbers go from 0 to 3.
Is Slitherlink good for beginners?
Yes. The first boards are small and the rules are short. Quirk has hints, undo and reset when you get stuck.
Related puzzles
Playing it in Quirk
Tap a side to draw a line. Tap again to cross it out, and once more to clear it.
Drag along the dots to mark several sides at once. Every side you drag over gets the same mark as the first side.
