A LITTLE FOCUS. A FRESH START.
Play Kropki Sudoku
Play Kropki Sudoku free online. White and black dots reveal consecutive and double-value pairs, with notes, hints, and five difficulties.
Get the iPhone app
OneStop Sudoku, wherever you go.
Website saves stay in this browser and don’t transfer to the app.
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The game loads here. Choose a difficulty to start or resume a puzzle.
LEARN THE TWIST
How to play Kropki Sudoku
In this version, not all possible dots are shown. An unmarked pair may still be consecutive or doubled; do not use missing dots to eliminate candidates.
The rules
Fill each row, column, and 3×3 box with 1–9, without repeats. White dots join consecutive digits; black dots join digits where one is twice the other. Not all dots are shown: unmarked pairs have no extra restriction.
A useful first move
Black dots allow only the pairs 1–2, 2–4, 3–6, and 4–8. Use these short candidate lists as a starting point, then consider connected dots together.
A white dot beside a 4 means its neighbor is 3 or 5. A black dot beside a 4 means its neighbor is 2 or 8. Other Sudoku restrictions can decide which one fits.
SOLVE IT STEP BY STEP
Follow a chain one dot at a time
Kropki dots describe the relationship between two neighboring cells. A black dot means one is twice the other; a white dot means their difference is one. A chain lets a conclusion from the first dot become an input for the next.
- Middle cell
- 3
- Last cell
- 2, 4
Resolve the black dot.
A digit paired with 6 by a black dot could be half of 6 or twice 6. Half is 3; twice is 12, which is outside Sudoku’s digit range. The middle cell is therefore 3.
Apply the white dot next.
The last cell differs from 3 by one, so it can be 2 or 4. The white dot does not tell you which direction the difference goes.
Keep both possibilities until another rule decides.
Use the last cell’s column and box to test 2 and 4. This chain alone has not solved that cell; writing both candidates is the correct stopping point.
Learn the short black-dot list
Within 1–9, the only unordered black-dot pairs are 1–2, 2–4, 3–6, and 4–8. A black-dot cell therefore cannot be 5, 7, or 9. The pair 1–2 satisfies both dot relationships, so neither dot color alone rules that pair out.
Common mistakes to avoid
- A black dot does not mean the larger digit must be on the right or below.
- OneStop does not show every possible dot. Undotted neighbors may still be consecutive or doubled.
Try the reasoning yourself
What can sit next to 4 across a black dot? What changes if the dot is white?
Show the answer and why
Across a black dot, the possibilities are 2 and 8. Across a white dot, they are 3 and 5. Crossing Sudoku units may remove some of these candidates.
Controls, difficulty, and saved games
Choose Beginner, Easy, Medium, Hard, or Expert above. Select an empty cell, then tap a number or use your keyboard. Notes let you pencil in candidates; three hints are available. Three mistakes end the puzzle.
Every mode and difficulty keeps a separate save in this browser. You can switch puzzles and return to your place. Clearing site data removes these saves; they do not sync with another device or the iPhone app. Settings include night mode and optional automatic cell advancement.
Correct entries earn points. High scores are stored by mode and difficulty and update only when beaten; completed-puzzle count and day streak are shared.
FIFTEEN WAYS TO PLAY
Explore all Sudoku modes
A familiar grid, a different kind of logic. Every mode is free to play in your browser.