Rules & objective
Draw straight horizontal or vertical lines only between adjacent dots. Each number 0–3 is the exact number of lines on that cell’s four sides; a blank cell has no count constraint. All drawn lines must form one nonempty closed loop, with no branches or self-intersections. Used dots have exactly two lines; unused dots may have none. You do not need to visit every dot. Matching the numbers in multiple separate loops does not win. Selecting an edge or hint only previews; press Draw or Apply to commit. Mark no line is an optional note; Clear removes either a line or note. These 90 original puzzles use 5×5, 7×7 and 9×9 grids, 30 of each with rotations/reflections. Their unique loop is verified from public clues. Hints use current marks, number sums, dot degrees and cycle constraints, never a stored answer. Confirm or cancel a hint. Check reports constraint consistency, not guaranteed correctness of each unfinished mark. Undo/redo restore real actions. Restart keeps this puzzle; New chooses another.
Controls
Play directly on the cards or board with mouse or touch. Coordinate selectors are optional keyboard aids.
Worked example
A clue of three requires exactly three of its four edges. All local clues must also combine into one continuous closed loop.