Loop Puzzle (Slitherlink)

How to play the Loop Puzzle

The Loop Puzzle is a logic puzzle from Japan. It is best known as Slitherlink. The board is a grid of dots. Some of the squares between the dots hold a number from 0 to 3.

Goal

Join dots with lines to make one single closed loop. The rules are:

• Lines go between two neighbouring dots, across or up and down. They never go diagonally.
• Each number tells you how many sides of that square are part of the loop. A 0 has no lines around it. A 3 has lines on three of its four sides.
• Squares without a number can have any number of lines.
• The loop may not cross or touch itself and may not branch. Every dot has either two lines or none.
• There must be only one loop.

Every puzzle here has exactly one answer and can be solved with logic.

Step by step

1. Tap the space between two dots to draw a line. Tap it again to remove it. You can also drag along the dots to draw several lines at once.
2. Switch to the Cross tool to mark gaps where a line cannot go. On a computer, right-click uses the other tool.
3. With the keyboard, click the board or press Tab to focus it. Move the dot cursor with the arrow keys and hold Shift with an arrow to draw from the cursor. Press T to switch tools.
4. A number turns dim when it has the right count and red when it has too many lines. A dot with more than two lines turns red. Press Undo to take back a move or a whole drag.

Levels

Easy is 6×6 and can be solved with simple local steps. Medium is 8×8 and Hard is 10×10, with fewer numbers, so you sometimes need to think ahead: "if a line went here, would it break?"

End of the game

The puzzle is solved when your lines form one closed loop and every number is met. The loop lights up and the timer stops. Your game is saved in this browser. For another line puzzle, try Bridges.

Strategy tips

• Start with the zeros. Put a cross on all four sides of every 0. Lines near a 0 must turn away from it.
• Look at corners. A 3 in a corner of the board always has lines on its two outside edges. A 1 in a corner has crosses on its two outside edges.
• Two 3s side by side. When two 3s touch along a side, the line between them and the two outer lines parallel to it are all part of the loop.
• Every dot has 0 or 2 lines. If a dot already has two lines, cross its other gaps. If a dot has one line and only one free gap left, the loop must continue through that gap.
• Avoid small loops. Never close a loop early. If one more line would close a small loop while other lines are still open, put a cross there.
• Use crosses a lot. Marking where lines cannot go is as useful as drawing lines. It makes the next step easy to see.