Slitherlink blog

Guides, history, and the math behind the Slitherlink loop puzzle. New here? Start with how Slitherlink works, then explore the rest. Prefer to just play? Jump in below.

• Slitherlink, Loop the Loop & Fences: A Puzzle With Many Names

  Slitherlink, Loop the Loop, Fences and Takegaki are all the same loop puzzle. Here's why this Nikoli puzzle has so many names, which name is used where, and how to recognise it.

• How Does Slitherlink Work? Why You Draw a Loop, Not Fill in Numbers

  How does Slitherlink work? Despite the numbered grid, you don't fill in numbers — you draw a single loop along the edges. Here's what the numbers mean and why it's unlike Sudoku.

• Puzzles Like Slitherlink: A Guide to Loop Puzzles

  Love Slitherlink and want more? Here's a guide to loop puzzles and other logic puzzles like it, from Masyu to Yajilin, and what makes the loop-puzzle family so satisfying.

• What Makes a Slitherlink Puzzle Hard?

  What makes a Slitherlink puzzle hard? Grid size, how many clues are given, and the mix of 0s and 3s all play a part. Here's what separates an easy loop puzzle from a brutal one.

• Do You Have to Guess in Slitherlink?

  Do you have to guess in Slitherlink? No — a well-made Slitherlink is always solvable by logic, thanks to the single-loop rule. Here's why, and how to find the next edge when stuck.

• The History of Slitherlink: Nikoli's Loop Puzzle

  The history of Slitherlink: how the Japanese publisher Nikoli created this loop puzzle, what its original name Takegaki means, and how it spread around the world as a logic classic.

• The Graph Theory Behind Slitherlink: Loops, Edges & the Inside-Outside Trick

  Slitherlink is a graph theory puzzle in disguise. Here's the maths behind the loop — cycles, the inside-outside trick, and why this simple-looking puzzle is NP-complete.

• How Slitherlink Puzzles Are Made (and Why They Have One Solution)

  How are Slitherlink puzzles made? Inside the construction process: drawing a loop, deriving the number clues, thinning them out, and guaranteeing a single solution solvable by logic.