Select White (○) or Black (●) mode, then click cells on the grid to place pearls. Click an existing pearl to cycle through states (white → black → empty). Once all pearls are placed, click Solve.
The solver uses constraint propagation — the same logic a human solver applies: at each pearl, the two possible entry/exit directions are restricted by the pearl rules, and those restrictions propagate along the loop. Backtracking resolves any remaining ambiguity.
White pearl ○: loop goes straight through, must turn in an adjacent cell.
Black pearl ●: loop turns here, must go straight through both adjacent cells.