What Is Slitherlink?
Slitherlink is one of Nikoli's original loop puzzles and first appeared in Puzzle Communication Nikoli issue 26 in June 1989. The grid gives you dots, numbered cells, and one job: draw a single closed loop. A clue tells you how many sides of that cell belong to the loop. The puzzle trains local counting and global shape control at the same time. Short segments must eventually become one loop, with no branches and no separate cycles. Start drawing edges and closing gaps.
How to Play Slitherlink
- Look at each numbered cell. The number tells how many of its four sides must be loop edges.
- Draw confirmed edges between neighboring dots.
- Mark confirmed non-edges when a side cannot be used.
- Keep all line segments connected into one final loop.
- Avoid branches, loose ends, and small separate loops.
- Finish when every clue is satisfied and the loop closes once.
Basic Rules
- A 0 cell has no loop edges around it.
- A 1 cell has exactly one loop edge.
- A 2 cell has exactly two loop edges.
- A 3 cell has exactly three loop edges.
- The final line must form one continuous loop.
- The loop cannot cross, branch, or end early.
Strategy Tips for Beginners
- Start with 0 clues. Mark all four sides as unused, then use those marks to solve nearby clues.
- A 3 beside a 0 forces the three sides away from the 0 in many common positions.
- Never let a dot have three line segments. Each loop dot can use only two edges.
- Avoid closing a small loop before all clues connect to it.
- Use corner pairs. Adjacent 3s near an edge often force long outside segments.
Real Examples of Gameplay
Zero Cell
A cell marked 0 cannot use any of its sides. Marking those four non-edges may force nearby 3 cells to use their remaining sides.
Dot Degree
A dot already has two line segments. Every other edge touching that dot must be marked unused, or the loop would branch.
Small Loop Warning
Four segments almost close a tiny square, but many clues remain outside it. Leave one side open until the main loop can include the rest of the grid.
Variations of Slitherlink
- Bridges: Also builds a connected network, but uses numbered islands and straight bridges.
- Nurikabe: Uses grid connectivity with shaded sea cells instead of loop edges.
- Masyu: A loop puzzle that uses black and white pearl clues.
Why People Love Slitherlink
- The numbers 0 through 3 create many strong patterns.
- The single-loop rule adds whole-board tension.
- Progress is visible as the line grows.
- Solvers can learn reusable patterns without memorizing long formulas.
Play Slitherlink Online for Free
Play Slitherlink online for free. Draw one loop, satisfy every clue, and use non-edge marks to prevent branches and early cycles. Small grids are best for learning the core patterns.
Comparison
| Version | Difficulty | Players | Typical Time |
|---|---|---|---|
| Small Slitherlink | Easy | 1 | 5 to 10 min |
| Standard Slitherlink | Medium | 1 | 10 to 20 min |
| Large Slitherlink | Hard | 1 | 20 to 35 min |
Frequently Asked Questions
Can Slitherlink have more than one loop?
No. The final answer must be one continuous loop.
What does a 3 clue mean?
Exactly three of the four sides around that cell must be line segments.
Why mark non-edges?
Non-edge marks stop branches and help nearby numbered cells reach their exact counts.
Start Playing Now
Slitherlink is a compact loop puzzle with rich logic. Count edges, block impossible sides, and keep every segment part of one final loop.