Slitherlink Puzzle

How to Play Slitherlink

Slitherlink is a drawing puzzle with one goal: draw a single closed loop along the grid lines that run between the dots. The loop can wander anywhere it likes, but it must obey two iron rules — it never crosses itself, and it never branches: every dot on the board is touched by either zero or two line segments. When the loop is finished, one continuous ring connects the whole puzzle.

The numbers steer you. A number in a cell tells you exactly how many of that cell's four edges are part of the loop:

• A 3 cell has exactly three of its four sides drawn.
• A 2 cell has exactly two of its sides drawn — any two.
• A 1 cell has exactly one side drawn.
• A 0 cell has none of its sides drawn — all four stay empty.

On GridPaw, simply click a line segment between two dots to draw it in amber, and click it again to erase. The clue numbers do the rest: once you place enough segments, the loop almost draws itself. Every puzzle here has exactly one valid solution, and you have 3 hints if you ever paint yourself into a corner.

What Is Slitherlink? Loop Puzzle Family

Slitherlink belongs to the family of loop-drawing puzzles that blossomed in Japan in the 1980s. It was invented by puzzle designer Naoki Inaba and first published by Nikoli — the same publisher that named Sudoku — in its magazine in 1989. Nikoli's founders wanted a puzzle about drawing one continuous line, and Slitherlink became one of their flagship titles, beloved for how a handful of small numbers can force a surprisingly elegant closed ring.

Like many Nikoli puzzles, Slitherlink travels under several names depending on the publisher and region. You will meet it as Slither Link, Loop the Loop, Fences, and in Japan as Suria no Kirinai — the name translates roughly to "the loop without dead ends", which is a wonderful description of the end state. The rules are identical under every name: one closed loop, numbers count their cell's edges, no crossings, no branches. Its closest cousins in the family are Masyu (black-and-white pearl clues) and Corral, but Slitherlink's elegant numeric clues make it the most approachable entry point.

Slitherlink vs Sudoku

Sudoku fills a grid with digits; Slitherlink draws a line — but the two puzzle families share a deeper DNA. Both are pure logic puzzles with a single valid solution, both reward systematic scanning over brute force, and both were popularized by Nikoli. The big difference is what you deduce.

In Sudoku every constraint is local and symmetric: each row, column and box must contain 1–9 exactly once. In Slitherlink the clues are local too — a 3 only governs its own cell — but the solution is one global object: a single loop. You cannot satisfy each number independently and hope the board works out; the loop has to close on itself, which forces you to reason about corners, dead ends and connectivity across the whole grid. Where Sudoku is bookkeeping with nine digits, Slitherlink is geometry with a pencil.

That difference makes the two puzzles perfect training partners. Sudoku sharpens categorical memory and candidate elimination; Slitherlink sharpens spatial reasoning and step-by-step deduction — staring at two adjacent 3s and knowing, with total certainty, which edge must be drawn.

Slitherlink Tips and Strategy

New to loop puzzles? These four techniques get you through almost any Slitherlink grid, from a 5×5 warm-up to a stubborn 10×10:

1. The 0-corner rule. A 0 clue is a gift: all four of its edges must stay empty. Erase them mentally (or tick them off) and watch the neighbouring numbers tighten up. Empty cells print nothing — but a 0 always prints, so it is easy to spot.
2. Adjacent 3s. Two 3 cells sharing an edge force that shared edge to be drawn — with four remaining sides between them needing five segments, every other edge of both cells is drawn too. It is one of the fastest deductions in the game.
3. Diagonal 3s. Two 3s touching at a corner lock the two edges that meet in the corner between them, and force the far corners' outer edges. If you see a diagonal pair of 3s, solve it before anything else — it usually unlocks a whole region.
4. Count edges at every dot. Every dot must end with exactly 0 or 2 segments. If two segments already meet at a dot, every other segment touching that dot must stay off; if a dot already has one segment, its neighbours decide the second. GridPaw helps here: any dot that would reach degree 3 turns red instantly, so you can never accidentally branch.

Finish with edge counting: the loop is one ring, so segments form chains that must bend back and connect. When a chain runs toward a blocked corner, the next edge is forced. Rarely get stuck? The Hint button lights up the correct state of one edge — 3 per puzzle — and a new puzzle restocks them.