Kropki Sudoku
White dots = consecutive digits; black dots = one digit is double the other
Kropki Sudoku is fully playable. Choose a difficulty and start solving.
Kropki Sudoku places dots between pairs of adjacent cells. A white dot means the two digits differ by exactly 1 (consecutive). A black dot means one digit is exactly double the other (e.g., 2 and 4, or 3 and 6). Where no dot appears, neither condition applies. Some Kropki puzzles use the 'negative constraint' where the absence of a dot guarantees neither condition holds, giving even more information.
Like all Sudoku variants, Kropki Sudoku builds on the classic 9×9 foundation. Every row, column, and 3×3 box must contain each digit from 1 to 9 exactly once. The variant constraint is added on top of these standard rules, never replacing them.
If you're new to Sudoku, start by learning the basic rules and techniques before attempting variants.
Techniques Useful for This Variant
| Technique | How it applies |
|---|---|
| Pencil Marks / Notes | Essential for tracking candidates alongside the variant constraint |
| Obvious Singles | Cells narrowed to one candidate by the combined constraints |
| Hidden Singles | Digits with only one valid cell in a unit after variant elimination |
| Pairs and Triples | Locked candidates exposed by the additional constraint |