Slitherlink puzzles are wonderfully pure logic puzzles with simple rules, yet they can be surprisingly rich to solve. They’re also known as Takegaki, Loop the Loop, or Fences puzzles.
The goal
Each puzzle is a lattice of dots with number clues in some cells. Link adjacent dots so that:
- The value of each clue equals the number of links surrounding that cell.
- Empty squares may be surrounded by any number of links.
- When finished, the solution is a single continuous loop with no crossings or branches.
Core insight: 0 or 2 lines at each point
Every lattice point has either exactly two lines connected to it, or none. That single fact powers most beginner deductions:
- If three directions into a center point are already blocked, the fourth must be blocked too.
- On an edge (not a corner), if two directions are blocked, the third must be blocked.
- At a corner of the board, if one direction is blocked, the other must be blocked.
Corner patterns
- 1 in a corner: the two outer corner edges can be marked empty — a line entering that corner could not leave without using the 1 twice.
- 3 in a corner: the two outer edges must be filled.
- 2 in a corner: two lines must leave the 2 along the border.
Adjacent 3s
If two 3s sit next to each other horizontally or vertically, their shared edge must be filled, and the outer parallel edges usually fill as well. The path wraps in an “S” shape rather than continuing straight through.
Practice in the app
Ready to try? Open Slitherlink on iOS or Android — start with small 6×8 boards, then grow into daily giant challenges.