In brief: Masyu was developed by the Japanese puzzle publisher Nikoli. An early version with only white circles appeared in Puzzle Communication Nikoli issue #84 as Shinju no Kubikazari (“pearl necklace”). Black circles were added in issue #90, when it was renamed Shiroshinju Kuroshinju (“white pearls and black pearls”), and it took the name Masyu in issue #103.
Nikoli and the language-free puzzle
Nikoli, whose puzzle magazine launched in Tokyo in 1980, is the publisher best known for popularising Sudoku. Its quarterly magazine Puzzle Communication Nikoli is unusual: many of its puzzle genres are invented or refined by readers, who submit new ideas that the editors test, polish and publish. Genres that prove popular become regulars — Slitherlink, Heyawake, Nurikabe and Hashiwokakero all became classics this way.
Masyu fits a Nikoli ideal especially well: a puzzle that needs no numbers, letters or language, only shapes. Its entire rule set can be explained with two kinds of circle and a loop, yet it supports deep logic. That made it equally accessible to players everywhere.
Timeline
| Stage | Name | What changed |
|---|---|---|
| Puzzle Communication Nikoli #84 | Shinju no Kubikazari (真珠の首飾り, “pearl necklace”) | First version: a loop through white circles only. |
| #90 | Shiroshinju Kuroshinju (白真珠黒真珠, “white pearls and black pearls”) | Black circles added — the turning rule that defines modern Masyu. The two-colour version proved much more popular. |
| #103 | Masyu (ましゅ) | Renamed, replacing the long two-part name. |
Issue numbers follow the commonly cited account in the Wikipedia article on Masyu. Some secondary sources date the puzzle’s origins to around 1999–2000; we report issue numbers rather than exact years because publication dates vary between sources.
Where does the name “Masyu” come from?
The kanji 真珠 are read shinju and mean “pearl”. According to the story usually told, Nikoli’s president misread them as mashu. The slip became an in-joke around the office, and the joke name eventually replaced the puzzle’s unwieldy official title.
The spelling “Masyu” rather than “Mashu” reflects the Kunrei-shiki system of romanising Japanese, in which しゅ is written syu. You will sometimes see the puzzle spelled “Mashu” in English.
You may read that Masyu means “evil influence”. That gloss comes from 魔手 (mashu), an unrelated Japanese word with the same pronunciation. The puzzle’s name is about pearls — the circles on the grid.
Why black pearls changed everything
With only white circles, the solver has just one kind of constraint: go straight, then turn nearby. Black circles introduced the complementary constraint — turn here, then go straight — and the interplay between the two is where Masyu’s richest logic lives. Patterns such as adjacent black pearls, a black pearl flanked by diagonal whites, or a white pearl wedged beside a black arm only exist because both colours are present. See our strategy guide for these patterns.
Masyu and mathematics
Masyu is a constraint-satisfaction problem on a grid graph: the solution is a single cycle (a closed path that visits some cells exactly once) satisfying local rules at each pearl. In his paper “Pearl Puzzles are NP-complete”, Erich Friedman showed that deciding whether an arbitrary Masyu has a solution is NP-complete — in general, no known algorithm solves every large instance quickly. Published puzzles are designed to be solved by human logic in reasonable time, which is exactly how we build ours: every puzzle on this site is checked by a logical solver to have one solution reachable without guessing.
One famous mathematical idea makes a regular appearance in Masyu solving: the Jordan curve theorem, which guarantees that a closed loop divides the plane into an inside and an outside. In practice, that means the loop crosses any closed boundary an even number of times — a powerful tool on big boards.
Masyu in competitions
Masyu is a staple of competitive puzzle solving. It regularly appears at the World Puzzle Championship and in national qualifying events, as well as in online contests and puzzle-hunt style events, often alongside variants. Competition setters love it because a single, elegant rule pair supports a huge range of difficulty.
Variants
- Gray pearls — some circles are gray, and you decide whether each behaves as white or black.
- Toroidal Masyu — the grid wraps around, so the loop can exit one side and re-enter on the opposite side.
- Regional Masyu — the grid is divided into regions and the loop must turn at least once in each.
- Hexagonal Masyu — played on a hex grid, with pearls marking 60° or 120° turns.
Want to see how Masyu relates to its loop-puzzle cousins? Read Masyu vs. Slitherlink, Yajilin and other loop puzzles.
Sources and further reading
- Masyu — Wikipedia
- Masyu — Puzzles Wiki
- Atlas Obscura on Masyu and Nikoli
- Erich Friedman, “Pearl Puzzles are NP-complete”.