Pearl / Masyu
Where must the loop turn at black and white pearls?
At a black pearl, turn on the pearl and continue straight through the next cell in both directions. At a white pearl, go straight through it and turn in at least one immediately neighbouring cell along the loop.
Worked example
A white pearl does not require turns on both sides. One adjacent turn is enough, provided the rest of the single loop remains valid.
What to check on your board
Apply the rule above to your current board, then verify the remaining puzzle constraints. The example explains a local deduction; it is not a solution to every randomly generated board.
Checking your next move
Check the pearl cell first, then the cells immediately before and after it on the loop. Distinguish turning on the pearl from turning beside it. Once the local rule fits, trace onward to ensure those decisions can still join one continuous loop.
Using this reference
For Pearl / Masyu, read the rule and the worked example together before opening the game. Separate what the rule explicitly requires from what only seems likely on the current board. A useful next move is one you can explain from the visible constraints, not merely a pattern that looks familiar.
If you get stuck, isolate a smaller part of the position and list what is still possible there. After a move, check the affected rows, regions or connections again. The reference explains the documented rules; progress, controls and save behavior belong to the linked game.
Read the developer’s manual ↗ · Open the developer’s browser version ↗
Manual inspected: · Simon Tatham & contributors · MIT