Diagonal Sudoku (Sudoku X)

Standard sudoku plus one extra rule: both main diagonals must also contain 1 to 9 exactly once. That small addition tightens every elimination chain and rewards whole-board vision.

Rules

• Every row, column and 3×3 box contains 1-9 with no repeats.
• The main diagonal (top-left to bottom-right) must be a permutation of 1-9.
• The anti-diagonal (top-right to bottom-left) must also be a permutation of 1-9.
• Both diagonals pass through the centre cell, so it carries four constraints at once.

Solving Tips

• Scan the diagonals first — digits there cannot repeat along the line, often pinning a single cell.
• The centre cell (r5c5) belongs to both diagonals; it is the strongest constraint on the grid.
• Treat each diagonal as a fourth unit alongside rows, columns and boxes.
• Because the constraint set is stronger, diagonal puzzles need fewer clues than standard ones.