Play Slitherlink — Free

What is Slitherlink?

Slitherlink is a pure logic puzzle played on a rectangular lattice of dots. Scattered among the cells between those dots are small numbers, and your job is to draw edges — short line segments connecting neighbouring dots — so that each numbered cell is bordered by exactly as many drawn edges as its number says. There is no arithmetic and no guessing: everything you need is printed on the grid, and when a puzzle is finished all of the edges you have drawn join together into one single, continuous loop that wanders around the board like a length of string with its two ends tied. It is quiet, elegant and quietly addictive — the kind of puzzle you start "just to try one" and finish a coffee later.

The game was created and popularised by Nikoli, the famous Japanese puzzle publisher that also gave the world Sudoku, and it goes by several names. In English it is most often called Loop the Loop or Fences, and you will also see it sold as Loopy, Dotted Loop, Slither Link and, from its original Japanese, Takegaki. Whatever it is called, the rules never change: match every number, and make one closed loop that has no loose ends, never branches and never crosses itself. On vygam we use the plain name Slitherlink, and every one of our puzzles is hand-authored with a real, verified solution, so you never have to guess — if an edge feels forced, it almost certainly is.

How to Play Slitherlink

The loop rule is strict, and several patterns are simply never allowed in a finished grid. A position is wrong whenever:

• any numbered cell has more or fewer edges around it than its number demands — the count must match exactly;
• a dot has only one edge touching it — that is a loose end, and a loop has none; every dot must touch either zero or two edges;
• a dot has three or four edges touching it — that is a branch or a crossing, and a single loop never splits;
• the edges form two or more separate loops instead of one — every drawn edge has to belong to the same single ring.

Slitherlink Tips & Strategy

Slitherlink rewards small, provable deductions rather than trial and error. Once you learn a handful of forcing patterns you stop staring at the grid and start reading it, and the loop almost draws itself. These four techniques work on every board, from the gentle 5×5 openers to the denser 6×6 puzzles.

1. Start with the 0s and the 3s

   The extreme clues give up their secrets first. A 0 means none of its four sides are ever used, so immediately mark all four with an X — that instantly settles four edges and often forces the neighbours around them. A 3 is nearly as generous: three of its four sides must be drawn, so as soon as you can rule out one side (because an X sits there) the other three are guaranteed. Cash in every 0 and 3 you can before touching anything else, and large parts of the board fall into place on their own.

2. Handle adjacent 3s and 3s in corners

   Two 3s side by side are a gift: the edge between them is always drawn, and so are the two outer edges on each far side, which fixes five edges in one move. A 3 tucked into a corner of the grid is even more rigid — the two sides that run along the board's edge are both forced, because the loop has nowhere else to go. Learn these little shapes and you will spot forced edges at a glance instead of reasoning them out from scratch every time.

3. Keep every dot legal — zero or two

   The single most useful running check is the degree of each dot: a dot on the finished loop touches exactly two edges, and a dot off the loop touches none. If drawing an edge would give a dot a third line, that edge is illegal. If a dot already has one edge and only one possible direction left, that direction is forced. Use X marks generously to record "no edge here" — every X you place removes a choice from a dot and pushes its remaining edges toward certainty.

4. X-out around a 0 and watch the walls

   Blank space is information too. Around every 0 you should cross out all four sides, and around a 1 you can often cross out sides that would otherwise force a second edge into a finished dot. Along the outer wall of the grid the loop can only turn inward, so edge cells with low numbers quickly become fixed. Alternate between claiming edges you can prove and X-ing out the ones you have ruled out, and even the hardest board unravels one certain step at a time — never a guess.

Reading the Loop

Every number in Slitherlink is a promise about the finished picture, and learning to read those promises is the whole game. Because the answer is a single loop, each dot behaves like a bead on a string: the string either passes straight through it, turns a corner at it, or misses it entirely, which is exactly why a dot can only ever end with zero or two edges. Holding that fact in mind turns a wall of numbers into a web of constraints — a 1 next to an X on one side has only three places left for its single edge, and a cell wedged against the border has fewer directions than one floating in the middle.

The connectivity rule is the part beginners forget, and it is where nearly-finished puzzles fall apart. It is perfectly possible to satisfy every number and still be wrong, because your edges have closed into two small separate rings instead of one big loop. Before you commit the last few edges, trace the path with your eye from any one edge and make sure you can travel the whole loop and return without lifting your finger. If a little ring has sealed itself off in a corner while the rest of the board is still open, something earlier has to change. Reading the loop as a single connected object, not just a set of satisfied numbers, is the skill that separates a quick solve from a stuck one.

Slitherlink vs Sudoku, Nonogram and Other Logic Puzzles

If you enjoy Sudoku, Nonogram, Kakuro or Bridges, Slitherlink will feel like a welcome new member of the family. Like all of them it is solved by deduction with no guessing required, and like the best of them it uses numbers only as clues rather than asking you to calculate anything. What makes Slitherlink distinct is what you are building: not a filled grid of digits or shaded squares, but a shape — a single closed loop that snakes around the board. The satisfying "aha" moments come from geometry and connectivity, from spotting that an edge is forced because every other route would strand a dot or break the loop apart.

That focus on a continuous line makes Slitherlink especially good on a touchscreen, where tapping the space between two dots to lay an edge feels natural and immediate. It also scales beautifully: a 5×5 grid with a scatter of numbers is a two-minute warm-up, while a 6×6 packed with 0s and 3s can absorb a whole break. Play a handful of levels and you will start to see the forced edges instantly, which is exactly the moment a clever little puzzle turns into a genuine test of foresight — and the reason Nikoli's Loop the Loop has kept solvers coming back for decades. Pair it with a game of Nonogram or Kakuro and you have a whole afternoon of quiet, guess-free logic.

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