SUDOKU VARIANT GUIDE
Kropki Sudoku: rules, strategy and how to start
White dots join consecutive digits, black dots join doubles. Two tiny marks, and suddenly the whole grid is about parity and spacing.
Why the rule changes everything
Black dots are severe: the only doubles are 1-2, 2-4, 3-6 and 4-8. That means 5, 7 and 9 can never touch a black dot — a single black dot eliminates three digits from two cells.
White dots are gentler but they chain: a run of white dots is a run of consecutive values creeping one step at a time.
How to start a board
- Find black dots first and strike 5, 7 and 9 from both cells.
- On a white dot, mark both cells with the pairs the grid still allows.
- Look for a cell with two dots — one white, one black — the intersection is usually a single pair.
Common mistakes
- Treating undotted neighbours as constrained. In this version only marked pairs carry rules.
- Forgetting 4-8 is a legal black dot; players often stop at 3-6.
- Ignoring the interaction with boxes: a dot on a box border constrains cells that never share a unit.
Frequently asked questions
What is the difference between white and black dots?
White: difference of 1. Black: one digit is double the other.
Do I need to mark every dot myself?
No — the dots are given with the puzzle. You only interpret them.
Every board on this site is generated with a uniqueness check, so the puzzle in front of you has exactly one solution and every digit can be proved rather than guessed.
Play Kropki Sudoku ↗