How to Play Kropki Sudoku

Kropki Sudoku is a variant where dots appear between adjacent cells. A black dot means one of the two cells holds exactly double the value of the other. A white dot means the two cells hold consecutive digits (differing by 1). Standard Sudoku rules apply, and crucially: if there is no dot between two adjacent cells, they are guaranteed NOT to be consecutive and NOT to have a double relationship.

A black dot between two cells means one digit is exactly twice the other. For example: 1&2, 2&4, 3&6, 4&8. Note that 1&2 satisfies both black (1×2=2) and white (|2-1|=1) conditions — in Kropki Sudoku, a black dot is used when only the doubling relationship holds, not the consecutive one, unless specified otherwise.

A white dot between two cells means the digits differ by exactly 1: they are consecutive. Valid pairs are 1&2, 2&3, 3&4, 4&5, 5&6, 6&7, 7&8, 8&9. The order doesn't matter — either cell can hold the higher or lower digit.

In standard Kropki Sudoku, every possible black dot and white dot relationship is marked. This means that if no dot appears between two adjacent cells, you can be certain those cells are neither consecutive nor in a 1:2 ratio. This negative information is just as powerful as the positive dot clues.

Easy Kropki puzzles are accessible and make excellent teaching tools for the variant. Hard and expert puzzles are significantly more challenging than classic Sudoku because you must simultaneously track dot relationships and the negative no-dot constraint across every pair of adjacent cells.

Easy puzzles take 8–18 minutes. Medium puzzles run 18–35 minutes. Hard puzzles average 35–65 minutes and expert puzzles often exceed 90 minutes. Mastering the no-dot constraint is the key to faster solve times at all levels.