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Slitherlink Guide: Loop Logic, Corner Clues and Solving Tips
Slitherlink is one long chain of small if-then steps, and the fastest solvers rarely guess, because corners, zeros, and vertex rules hand them the edges for free.
1. The loop lives on the lines between dots
Slitherlink is drawn on a lattice of dots, and the loop travels along the short segments that join neighbours. Every numbered square tells how many of its four sides the loop uses: a 3 means three belong, while a blank cell says nothing.
Use the Line tool to draw a segment or the Cross tool to declare one impossible; clicking a mark again lifts or converts it, so you never need a separate eraser.
- Crosses are real information: they record that an edge is definitely not part of the loop and keep your deductions honest.
2. Two silent rules govern every dot
Whatever the numbers say, the drawing obeys two silent rules. A dot may carry zero or exactly two loop edges, so the loop never branches or crosses itself, and the whole drawing must close as one single shape.
A dot with two edges decided is finished, forcing every remaining edge off; a dot with one edge is a loose end that must gain a second, and each decision removes options from its neighbours.
- The game flags three or more lines meeting at a dot in red, so treat that warning as an immediate undo.
3. Start from the 0 cells and let crosses spread
Cells marked 0 are the classic entry point: cross all four of their sides at once. Those crosses touch neighbouring cells and dots, subtracting from clue counts and closing vertices.
Feed it forward: a cell whose drawn sides match its clue has the rest crossed, and one whose drawn plus open sides exactly equal its clue forces its last open side on.
- A 0 cell sharing an edge with a 3 cell crosses that edge for the 0, leaving the 3 with three sides that must all become lines.
4. The corners of the grid are the easiest reads
The rim hands you cheap information, since a corner dot has only two edges and an edge dot only three.
In an actual board-corner cell, clue 0 crosses all four sides; clue 3 draws both border edges plus exactly one inner edge; clue 1 crosses both border edges, leaving the lone loop edge as one of the two inner sides, because the corner dot can never carry a single dangling line.
- Once a border edge is decided, its dots constrain the neighbouring rim cells, so deductions walk down the edge of the board.
5. Budget a cell's four sides like coins
Treat each numbered cell as a budget of four sides. When drawn sides equal the clue, cross the rest; when drawn plus undecided equals the clue, the last undecided side is forced to be drawn.
Respect the 2 cells, the most flexible and most frequent. A 2 rarely decides itself, but once two of its sides are crossed, both surviving sides must be drawn.
- A 3 that loses one side has three forced edges, which usually drags a whole line of segments along with it.
6. Grow arcs and never strand a loose end
As lines grow into arcs, guard the loose ends. A dot holding one line must eventually meet another arc end, so never cross off its last remaining open side. Keep the drawing as one or two growing paths and steer their ends toward each other.
Nor may you close a small ring early while numbered cells lie outside it, because that strands a second loop that can never join. Undo the closing segment and route the ends around instead.
- Before drawing any edge, glance at its two end dots: an end that already carries two lines cannot accept one more.
7. From 5×5 warm-ups to 9×9 loops
Warm up on Easy 5×5, where the corner reads above usually finish the loop in minutes; Medium is 7×7 and Hard 9×9.
Think of the loop as territory, the border of a region of cells: runs of small clues often mark long straight borders, while tight clusters of 0s and 3s pinch it into corners. Fill the sure segments first and let Undo make guessing cheap.
- Daily Slitherlink serves the same medium 7×7 board to everyone, so mastering that shape doubles as daily practice.