Rules & objective
Draw horizontal or vertical lines between adjacent cell centres to form one nonempty loop, without crossings or branches. Visit every black and white pearl; blank cells are optional. Go straight through a white pearl and turn at a right angle in at least one immediately neighbouring cell along the loop. Turn at a black pearl, then go straight through both immediately neighbouring cells, reaching the second cell centre on either side. We made 30 original puzzles each at 5×5, 7×7 and 9×9, with rotations and mirrors; uniqueness is verified from public pearls and one-loop constraints. Selection and hints only preview; confirm Line or Apply to change marks. Absent-edge notes are editable; Erase removes a line or note. Hints derive from visible clues and marks, without stored answers. Check reports constraint conflicts, not guaranteed correctness of unfinished marks. Restart keeps this puzzle; New changes it.
Controls
Play directly on the cards or board with mouse or touch. Coordinate selectors are optional keyboard aids.
Worked example
A black pearl requires a turn and the adjacent straight segments. A white pearl requires straight passage with a turn on at least one adjacent side.