Mouse
- Click an edge: toggle line / X mark
- Drag: draw multiple edges (if supported)
- Right click: toggle X mark (if supported)
Overview 
Slitherlink
일필휘지-싱글 라인 루프
Connect the dots to form one loop that matches every numbered cell.
A single loop, no dead ends—numbers quietly dictate where the fence must go.
Logic PuzzleLoop Puzzle
Goal & Core Rules
Draw a single continuous loop along the grid lines so that each numbered cell has exactly that many of its sides used by the loop.
- Draw lines between adjacent dots (horizontally/vertically) to form a single loop.
- The loop cannot branch and must have no loose ends.
- A number in a cell tells how many of its four sides are part of the loop.
- All numbered cells must be satisfied.
Controls
Keyboard
- Arrow keys: move cursor (if supported)
- Space/Enter: toggle line (if supported)
- X: toggle X mark (if supported)
Touch
- Tap: toggle line / X mark
- Drag: draw multiple edges (if supported)
- Long-press: toggle X mark (if supported)
Beginner Tips
- Start with 0s and 3s—they immediately forbid or force edges around a cell.
- Mark impossible edges with X to avoid accidental branching later.
- Follow the loop rule: any vertex can have degree 0 or 2—never 1 or 3.
Advanced Tips
- Avoid premature small loops unless you’re sure the entire loop is complete.
- Use parity/region reasoning: a loop must enter/leave areas in balanced ways on many grids.
- When you force an edge, immediately propagate vertex constraints two steps out.
Origins & History
Slitherlink is a Nikoli logic puzzle that first appeared in Puzzle Communication Nikoli issue #26 (June 1989). It also became known internationally under many alternate names such as Fences and Loop the Loop.
Timeline
- 1989 First appeared in Puzzle Communication Nikoli (issue #26, June 1989).
FAQ
Can the loop touch itself?
It can touch at corners, but it cannot cross or branch.
What do numbers 0 and 3 mean?
0 forbids all four sides; 3 forces three of the four sides to be in the loop.
What if I create two separate loops?
That violates the ‘single loop’ rule—merge them or undo the closure.