How Do You Play Slitherlink (Loop the Loop) on puzzle-loop.com?

Slitherlink on puzzle-loop.com is a logic puzzle where you draw lines between dots to form one single closed loop with no crossings or branches. Each number tells you how many of the four edges around it are part of the loop. Left-click between dots to connect them, right-click to mark an edge with an X as definitely not part of the loop. Start with 0s and 3s, then work outward using the constraints each number places on its neighbors.

The Rules in Plain Terms

The board is a grid of dots. The loop runs along the gaps between dots, so every edge you draw is a segment connecting two adjacent dots.

• One loop only. The finished line must be a single closed circuit. No separate loops, no dead ends, no branches.
• No crossings. Lines may meet at dots, but they never cross each other.
• Numbers count surrounding edges. A number sits inside a cell. Its four sides are the four edges around it. The number tells you exactly how many of those four edges are drawn.
• Blank cells have no constraint. A cell with no number can have any number of drawn edges from 0 to 4.

A 0 means none of its four sides are drawn. A 3 means three of the four are drawn, so only one is excluded. These two extremes are the most informative starting points.

How to Draw and Mark on puzzle-loop.com

The site uses a two-button scheme that maps directly onto the logic:

• Left click between two dots to connect them with a line segment.
• Right click between two dots to place an X, marking that edge as definitely not part of the loop.

X marks are your scratch work. They record deductions so you don't re-check the same edge. The site also offers optional aids you can toggle, including auto-crossing the sides of completed numbers, graying out completed numbers, highlighting wrong moves, and a ghost lines mode.

A Basic Solving Sequence

Work from the most constrained cells to the least. A practical order:

1. Fill in the forced edges around 0s and 3s. Every side of a 0 gets an X. A 3 forces three lines and one X, but which three depends on neighbors — often you can only mark the X once you see the surrounding constraints.
2. Apply the 2 rule at corners and edges. A 2 in a corner cell has only two possible edges, so both are drawn. A 2 on the board edge has three possible edges, meaning exactly one is excluded.
3. Use the no-branch rule at every dot. A dot in the loop has exactly two drawn edges meeting it — never one, never three. This single rule eliminates many possibilities as you go.
4. Propagate from neighbors. When a cell's count is already satisfied, X out its remaining sides. When a cell has only enough open edges left to reach its number, draw them all.
5. Watch for premature loops. If a drawn path closes on itself before covering the whole board, some segment in it is wrong. Backtrack and re-examine.

Repeat these steps; each pass through the grid usually unlocks new forced moves.

Sizes, Difficulty, and Special Puzzles

puzzle-loop.com offers a range of board sizes, each in Normal and Hard:

There are also Daily, Weekly, and Monthly special puzzles, plus a specific-puzzle lookup by ID and a mass print option. If you want to learn the mechanics without time pressure, start at 5x5 Normal.

Built-in Tools Worth Using

The site includes a timer and checkpoints, and you can switch the timer to a non-competitive personal mode. Other options that help while learning:

• Show checkpoints to track progress.
• Highlight last change so you can see what you just did.
• Magnify part of the puzzle while drawing for large boards.
• Highlight wrong numbers / wrong moves to catch mistakes early.
• Dots style (normal, smaller, tiny) to fit more of the grid on screen.
• Night mode and left-handed layout.

The game requires JavaScript enabled in your browser to play online, though you can print a copy instead.

Common Sticking Points

• Marking X too late. Placing Xs as you eliminate edges keeps the board readable and prevents contradictions.
• Forgetting the single-loop rule. A valid partial path that forms a small closed loop is already wrong, even if every number checks out locally.
• Ignoring edge and corner cells. Cells on the border have fewer possible edges, so their numbers are more restrictive and often resolve first.
• Treating 1s and 2s as unhelpful. They rarely force edges alone, but combined with a neighbor's count they often do.

Once you can clear a 5x5 Normal consistently, move to 7x7 and then 10x10. The logic scales; only the bookkeeping grows.