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.
Outside Sudoku places digits in the margins of the grid. Each outside digit must appear in one of the first three cells (the nearest box) of the row or column it points to. No standard given digits are provided inside the grid — all clues come from the margins. This creates an unusual form of Sudoku where the initial constraints come from outside the grid entirely.
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 |