X-Sudoku
Classic rules, plus a hidden twist: each of the two main diagonals must also contain every digit 1–9.
What makes it X-Sudoku
The two main diagonals — top-left to bottom-right and top-right to bottom-left — become unique units in their own right. That's 11 constraints per cell on the diagonals, instead of the usual 3. It changes which cells become naked or hidden singles, and which cells the early eliminations land on.
Same total puzzle space as classic, but the diagonal logic is what unlocks them. If you're a classic player, X-Sudoku rewards thinking about the diagonals before the boxes.
Rules
- All classic rules: rows, columns, 3×3 boxes each contain 1–9.
- The top-left to bottom-right diagonal contains each digit 1–9 exactly once.
- The top-right to bottom-left diagonal contains each digit 1–9 exactly once.
How Stillgrid plays
- Diagonal cells visually highlighted so you don't forget the extra constraint.
- Pencil marks, auto-pencil, undo/redo.
- Difficulty graded against the diagonal-aware solver.
- No signup. No ads.