How to Play Slitherlink

Slitherlink is a loop puzzle. The board is a grid of dots, and your job is to draw a single continuous loop that doesn't cross itself or branch. Numbers inside cells are clues — they tell you exactly how many of the four edges around that cell belong to the loop.

The Puzzle

Here is a 5×5 puzzle. Cells with numbers are clues; blank cells have no constraint.

The Three Rules

Rule 1: A clue tells you how many of its 4 edges are part of the loop

A cell with a 2 has exactly 2 of its surrounding edges drawn. A 3 has 3. A 0 has none. A 1 has one. Blank cells have no constraint.

Rule 2: The loop is one continuous closed curve

No branches, no separate loops, no dead ends. Every corner dot on the board ends up with either 0 edges (not part of the loop) or exactly 2 edges (the loop passes through).

Rule 3: The loop doesn't cross itself

Two edges meeting at a corner means “turn here” or “pass through here”. Three or four edges at the same corner would create an intersection — forbidden.

Two Foundational Techniques

Technique 1: A 0 forbids all 4 surrounding edges

It's the cleanest possible deduction. A 0 cell can have no edges on it — period.

Technique 2: A 2 sandwiched by two 0s forces the other two edges

When a cell with clue 2 sits next to two cells with clue 0 on adjacent sides, those two 0s “use up” two of the 2's edges (forcing them to NOT be drawn). The remaining two edges of the 2 must both be drawn to satisfy its count.

Walkthrough

Step 1 — Apply every 0 clue

Our puzzle has five 0 clues at (1,5), (3,2), (4,3), (4,4), (5,3), and (5,5). Each forbids its 4 surrounding edges. That immediately eliminates a huge portion of the candidate edges.

Step 2 — The 2 at (4,3) is sandwiched by two 0s

The cell with clue 2 at row 4, column 3 has 0s at row 4, column 4 (to its right) and row 5, column 3 (below it). Both of those 0s force the right and bottom edges of the 2 to be empty. The 2 still needs 2 edges, and only the top and left remain. So both must be drawn.

Step 3 — Continue cascading

Each new edge has consequences. The two newly drawn edges create two new corner dots that now have exactly 1 edge — and corners must have either 0 or 2 edges in a valid loop, so each one needs another edge added. That forced edge then propagates further. On easy puzzles, these chains complete the entire loop without guesswork.

Continuing the deductions yields the unique solution:

Tips for Beginners

• Mark forbidden edges with an ✗. Knowing what can't be drawn is as useful as knowing what must be. The 0 clues hand you many ✗s for free.
• Look at corners. Every corner dot needs exactly 0 or 2 edges. If 3 of 4 surrounding edges are forbidden, the 4th must also be forbidden (you can't reach 2). If 1 of 4 is drawn, one more must come.
• Use diagonal-clue patterns. A 0 diagonally adjacent to a 3 forces specific edges around the 3. Look these patterns up when you stall.
• Check loop closure. Even if all clues match, a partial loop or two separate loops is invalid. Always verify there's exactly one continuous closed curve.
• Don't guess. Easy puzzles never need guessing. If you're stuck, look for a corner or a clue cell whose edges are partially decided.

Ready to try one yourself? Hit the button below to play your first Slitherlink.