Does the loop have to touch every dot?

No. Dots it doesn’t need are left alone. Each dot has either two lines or none.

What do squares without a number mean?

Nothing is known about them: the loop may use any number of their sides.

Do I ever need to guess?

No. Every Slitherlink on this site has exactly one answer, and each one is checked to be solvable step by step without trial and error.

What are the crosses for?

A cross marks a gap where the loop definitely doesn’t go. Tap a gap twice to place one. They aren’t needed for the answer, but they make the next steps much easier to see.

How big are the puzzles?

The daily Slitherlink is 8×8. Practice puzzles come in 5×5, 7×7 and 10×10.

How to play Slitherlink (Loopy): rules, tips and FAQ

Watch one get solved

DemoStep through a small Slitherlink being solved. Each move follows from one rule, and the ring shows which clue it comes from.A 0 uses none of its four sides, so cross them all out. Each cross tells the dots beside it which ways the loop can’t go.A corner dot of the grid has only two sides, so the loop uses both or neither. A 3 in a corner needs both: two lines at the top right and two at the bottom left.Every dot has two lines or none. The 0’s top-right and bottom-left dots have just one gap left, so no line can use them: cross those gaps. Now the corner lines can only turn inwards.Both 3s now have three lines. A number that’s met can’t use any more sides, so cross out the fourth side of each.At the top-left corner of each 3, the new cross leaves the line just one way to go. A line can’t stop at a dot, so it carries on: left along the top, and up the left side.The 1 at the top now has its one line, so it’s met. Cross out its other sides.Follow the loose ends. The top one can only go left and down the corner, meeting the line on the left. The other can only go down to the 0, which turns it left. That’s one loop. Solved!

Using the board

Drag from dot to dot to draw the loop. Drag back over a line to erase it.

Tap the gap between two dots to cycle through line, cross and empty. A cross means “no line here”. Right-click puts a cross straight away.

A number turns grey once it has exactly the right lines around it, and red if it has too many or can’t be met.

Lines turn red where three meet at a dot, or where a closed loop leaves other lines out.

What is Slitherlink?

Slitherlink is a loop puzzle on a grid of dots. You join neighboring dots with lines to make one single loop, with no crossings and no branches. Numbers inside the squares say how many of that square’s four sides the loop uses.

It was published by Nikoli, and it’s also known as Loopy and Fences. The rules fit in two sentences, but larger puzzles can take real thought, which is why it’s one of the most popular Japanese logic puzzles worldwide.

How to start a Slitherlink

Cross out every side of each 0 first. Crosses are as useful as lines: each one tells the dots next to it which ways the loop can’t go.

Then look at the 3s. A 3 next to a 0 uses its other three sides. Two 3s side by side always use the side between them and both far sides. A 3 in a corner of the grid uses both corner sides, and a 1 in a corner uses neither.

After that, work dot by dot. The loop passes straight through dots, so each dot ends up with two lines or none. A line that reaches a dot with only one way out must take it, and a dot that already has two lines gets crosses on its other sides.

A trick for harder puzzles

Every square is either inside the loop or outside it, and crossing a line always takes you from one to the other. Squares outside the grid count as outside. When you know two neighboring squares are on the same side, the line between them must be crossed out; when they’re on opposite sides, it must be drawn.

Questions

Does the loop have to touch every dot?: No. Dots it doesn’t need are left alone. Each dot has either two lines or none.
What do squares without a number mean?: Nothing is known about them: the loop may use any number of their sides.
Do I ever need to guess?: No. Every Slitherlink on this site has exactly one answer, and each one is checked to be solvable step by step without trial and error.
What are the crosses for?: A cross marks a gap where the loop definitely doesn’t go. Tap a gap twice to place one. They aren’t needed for the answer, but they make the next steps much easier to see.
How big are the puzzles?: The daily Slitherlink is 8×8. Practice puzzles come in 5×5, 7×7 and 10×10.

Play today’s Slitherlink Solving techniques

The rules