Outside Sudoku
Digits outside the grid must appear in the first three cells of that row or column
Outside Sudoku is fully playable. Choose a difficulty and start solving.
Digits printed in the margins must land within the first three cells of the row or column they face. Each clue defines a small window, and overlapping windows pin digits precisely. A gentle introduction to outside-clue solving — no arithmetic involved.
For the complete rules, worked examples and solving techniques, read the full How to Play Outside Sudoku guide.
Like all Sudoku variants, Outside 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 |