How to Play Slitherlink

Slitherlink, also called Loop the Loop or Fences, is a logic puzzle played on a grid of dots. Some squares hold a number. Your job is to draw one closed loop along the dotted lines so that every number is right.

The rules

Draw a single loop by joining neighbouring dots with lines, across or down. No diagonals.
The loop never branches and never crosses or touches itself: at every dot it either passes through once or does not visit at all.
A number tells how many of the four sides of its square are part of the loop. A 0 has none, a 3 has three.
A square without a number can have any number of sides on the loop.

Every puzzle here has exactly one answer, and you can always reach it by logic alone. You never need to guess.

Controls

Tap or click between two dots to draw a line. Tap the same edge again to mark it with × (no line here), and once more to clear it. On a computer, right-click marks an × straight away.
Drag from dot to dot to draw several lines in one go. Dragging back along a line erases it.
Undo and Redo step back and forward through your moves, as far as you like. Start over clears the board.
The eye button shows or hides mistakes: a number with too many lines (or too many crosses) turns red, a number that is met turns grey, and a red dot marks lines that branch or stop at a dead end.
On a keyboard, the arrow keys move between dots. Shift plus an arrow draws or erases a line, Alt plus an arrow marks an ×. Z undoes, Y redoes.
On a phone, the 15×15 Expert board has a zoom button. Use two fingers to move around a zoomed board.

Difficulty

Level	Board	What it takes
Easy	5×5	Each step follows from one number or one dot
Medium	7×7	Reading two neighbouring clues together, like a 3 in a corner
Hard	10×10	Short “what if” chains: try a line, see a contradiction a few steps later
Expert	15×15	Longer chains of reasoning across the board

Difficulty comes from the kind of reasoning a puzzle needs, not just its size. Our solver checks every puzzle and sorts it by the hardest step it needs.

Solving tips

Start with the 0s. Every side of a 0 is an ×. Crosses tell you where the loop cannot go.
3s next to each other. Two 3s side by side share their middle edge, and their two outer edges are lines too.
Corners. A 3 in a corner of the board has both outer sides drawn. A 1 in a corner has neither. A 2 in a corner has its lines leaving the corner on both sides.
Follow the dots. A dot with two lines is done: cross out its other edges. A dot with one line must carry on, so if only one way is left, take it.
Do not close the loop too early. A line that would close a small loop while other lines are still apart must be an ×.
Inside and outside. The loop splits the board into inside and outside. Two squares on either side of a line are on different sides; two squares across a cross are on the same side.

Daily challenge

Every difficulty has as many puzzles as you like: finish one and the next is ready. On top of that, the Daily challenge has one new 10×10 puzzle every day. It changes at midnight on your own clock, and everyone in the world gets the same one. Solve it every day to keep your streak. Missed a day? Pick it from the calendar beside the board.

Questions

Do I need an account? No. Your progress and times are saved in your own browser.

Can I play offline? Yes. Once you have opened the site, you can add it to your home screen and keep playing without a connection.

Is it free? Yes, with no ads and no sign-up.

Who invented Slitherlink? It was first published by the Japanese puzzle publisher Nikoli in 1989. Loop Puzzle is an independent site and is not affiliated with Nikoli. All puzzles here are made by our own generator.