Slitherlink
Slitherlink is a loop puzzle on a grid of dots. Draw lines between neighbouring dots to make one single closed loop. A number in a cell tells how many of its four sides the loop uses; cells without a number can have any count.
How to play
Every Slitherlink here has exactly one solution and can be solved by logic alone. The grid grows from 5×5 at Easy to 10×10, and the level is set by the hardest technique the puzzle needs.
- Draw one continuous loop along the grid lines, with no branches and no crossings.
- A number counts how many of its cell's sides are part of the loop.
- The loop never touches itself: every dot has two lines or none.
Playing on this site
- Tap an edge to draw a line, tap again to cross it out, and once more to clear it.
- Drag from dot to dot to draw several lines at once; a drag that starts on a line erases instead.
- A number fades once it has all its lines.
- Crosses are only a helper: the puzzle is solved as soon as the loop is complete.
- Hint points out wrong lines and crosses first, then names the next technique and highlights the edges it decides.
- Your puzzle is saved in this browser, so you can come back to it later.
Techniques by level
Every technique the solver knows, from easiest to hardest. A puzzle's level is the hardest one it needs.
Easy
- Number count
- This number already has all its lines, or needs every side still open, so the marked edges follow.
- Dot rule
- The loop passes a dot with exactly two lines or not at all, so the marked edges follow.
- Closed corner
- The loop can't turn away at this shut-off corner, so a 1 takes neither corner edge and a 3 takes both.
Medium
- Adjacent 3s
- Two 3s side by side always have a line between them and on their outer sides.
- Diagonal 3s
- Two 3s on a diagonal always have lines around their two far corners.
- Early loop
- This edge would close a loop while other lines or numbers are still unfinished, so it stays empty.
Hard
- Corner flow
- Track how many lines can enter each corner of the highlighted cells; passed across dots and numbers, it settles the marked edge.
- Inside and outside
- Every cell is inside or outside the loop: a line separates the two sides and a cross joins them.
Expert
- Contradiction
- Leaving the marked edge empty breaks a rule a few steps later. So it must be a line.
Questions
Where should I start a Slitherlink?
Cross out the four sides of every 0. Then look at 3s: in a corner of the grid, two of their sides are certain, and two 3s side by side always share the line between them.
Will I ever have to guess?
No. Every puzzle has exactly one solution that logic alone reaches, at every level.
Is Slitherlink free to play here?
Yes. Every level is free, with no account and no sign-in.