How to Solve Masyu: White Pearls, Black Pearls, and Forced Turns

Updated August 2026

Masyu has two rules and almost no clutter: draw one closed loop through the centres of cells, and obey what the pearls demand. That minimalism is exactly why it feels hard at first — there is no number to count, only shapes to recognise. Once the handful of forced patterns are in your eye, boards that looked blank start solving themselves.

The rules, stated precisely

• Draw a single closed loop through cell centres, moving only horizontally and vertically, never crossing itself.
• The loop must pass through every pearl.
• At a white pearl the loop goes straight through, and it must turn in at least one of the two cells immediately before or after.
• At a black pearl the loop turns, and it must travel straight for at least two cells in both directions leaving the turn.

Read those two pearl rules twice. Almost every deduction in Masyu is a direct consequence of one of them meeting an edge, a corner, or another pearl.

Black pearls near an edge

A black pearl needs two clear cells in each of its two directions. So a black pearl on the border cannot travel toward that border at all — it must go inward, which fixes one of its two arms immediately. A black pearl one cell in from the border is the same story: there is not room for two cells that way. A black pearl in a corner region is often fully determined by this alone, giving you a confident four-cell start in a board that otherwise offers nothing.

White pearls in a row

The loop goes straight through a white pearl, so a run of white pearls in a line all share that line — the loop travels along the whole run. Now apply the second half of the white rule: the loop must turn just before or just after each pearl. With three white pearls in a row the middle one cannot get its turn inside the run, which forces the turns to the ends and fixes the geometry. Two white pearls adjacent to each other similarly force the loop to turn at both outer ends.

A white pearl on the border also cannot run perpendicular to the border, since half of that direction is off the grid — so it runs along the border, which usually chains into its neighbours immediately.

Black pearls cannot touch

Two black pearls orthogonally adjacent are impossible in a valid puzzle, so you will never see them — but the useful version is that a black pearl's two straight arms cover two cells each, and any pearl sitting in those cells constrains you hard. A white pearl exactly two cells from a black pearl in a straight line forces the black pearl's arm to run through the white one, which then must continue straight and turn beyond. Chains like this are where the middle game gets fast.

Rule out before you draw

Marking edges as forbidden is as valuable here as in Slitherlink. If a cell has three of its four sides ruled out, the loop cannot pass through it at all, or must use the remaining side twice — impossible. Cells the loop cannot enter act like walls and reshape everything nearby. Similarly, any cell with two loop segments already attached is finished; cross out its other two sides so you stop reconsidering it.

Finish with the single-loop rule

Near the end you will have several separate strands. The solution is one loop, so any join that would close a small loop while other strands remain is illegal. That single observation usually decides the last few ambiguous cells. It is also a useful sanity check earlier: if a set of forced moves would inevitably seal off a short loop, one of those moves was wrong.

A reliable order of attack

1. Place forced arms for every black pearl on or near a border.
2. Draw the straight lines through runs of white pearls and fix their end turns.
3. Extend black pearl arms two cells and mark the turn at the pearl.
4. Look for pearls sitting inside another pearl's forced arms and chain the consequences.
5. Cross out impossible sides; treat unreachable cells as walls.
6. Join strands, refusing any join that would close the loop early.

Masyu rewards pattern recognition more than calculation. Solve a few boards with these shapes in mind and you will start seeing the forced arms before you consciously reason about them.