Masyu

Overview

Masyu uses black and white pearls to constrain a single continuous loop. The loop travels through the centres of adjacent squares and must visit every pearl. At a black pearl it turns, and the squares immediately before and after that pearl must be straight. At a white pearl it travels straight, but at least one immediately neighbouring square along the path must contain a turn. Unmarked squares may hold straight segments, turns or no line at all. These paired rules make shape, rather than arithmetic, the central clue language. The locally compiled Pearl engine creates new Masyu boards and checks the result. As with other loop puzzles, a collection of separate rings is not a valid substitute for one loop through the entire set of clues. Borders matter enormously here, because pearls near an edge have fewer legal shapes.

How to Play

Drag between neighbouring squares to draw loop segments, or click the edge between their centres to toggle a segment. Use secondary input to mark an edge that the loop cannot cross. On a phone, short drags work well for a small sequence of cells, while individual taps provide finer control near crowded pearls. Visit every black and white pearl under its specific turning rule, without crossings or branches. Undo removes your latest drawing action. Restart resets the same puzzle, and New offers a freshly generated arrangement. When the board grows busy, mark impossible edges as actively as you draw real ones.

Tips & Strategy

Black pearls near a border have limited turning directions because both outgoing arms must continue straight for another square. White pearls next to one another can also constrain where a turn may occur. Draw forced extensions immediately, then revisit nearby pearls whose choices have narrowed. Be careful with the white rule: it needs a turn on at least one side, not necessarily both. Before closing a loop, check whether an unvisited pearl remains elsewhere. A visually elegant ring is still incomplete if it strands one clue or creates an additional disconnected piece of line.

Reading the Pearls

The strongest opening pattern is the black pearl one cell from a border. It must turn, and each arm has to run straight for a further square after the turn. If it turned toward that border, the arm would need a second square that does not exist, so the turn is impossible and the pearl must open parallel to the edge instead. A black pearl in a corner of two close borders is even tighter, often fixing both arms outright.

Rows of white pearls create the second classic pattern. Because the loop passes straight through each white pearl, a line running along a row of adjacent whites can only satisfy them if a turn falls immediately before the first pearl or immediately after the last one. A worked example: a black pearl sits one row below the top edge, so its arms extend horizontally, at least one square each way. A white pearl directly beside it on that row is now passed straight through, which means a turn must occur in a cell touching it — and since the black pearl's side is committed to a straight arm, the turn is forced onto the white pearl's other side. Two clues have just decided three cells of the path.

Errors That Break the Loop

Beginners frequently impose the black rule on white pearls by drawing turns at them, when the actual requirement is straight passage with a turn merely adjacent. The reverse slip is extending a black pearl's arm into an immediate bend; the square after a black pearl must stay straight. Another common failure is closing a pleasant ring early and discovering one pearl outside it. Finally, remember that most cells stay empty: forcing the loop through every blank square is not required, only through every pearl.

About this version

Masyu uses the locally compiled pearl engine from Simon Tatham’s Portable Puzzle Collection. The original authors retain credit under the MIT license. SonoTap provides the browser adaptation and this guide.