What is X-Sudoku?
X-Sudoku (or Diagonal Sudoku) is a classic 9×9 Sudoku with one extra constraint: the two main diagonals must also contain the digits 1 to 9 without repeating. That single added rule reshapes the entire logic of the puzzle and opens up deductions that don’t exist in standard Sudoku.
X-Sudoku rules
- All the standard Sudoku rules apply (rows, columns and 3×3 blocks).
- The main diagonal (top-left to bottom-right) contains 1 to 9 without repeating.
- The anti-diagonal (top-right to bottom-left) contains 1 to 9 without repeating.
Strategy
The diagonals act as two extra groups, so always check them alongside the usual rows, columns and boxes. The centre cell belongs to both diagonals at once, which often makes it the richest starting point for deductions.