X-Sudoku keeps the familiar 9×9 Sudoku School board and controls, but adds one extra rule: both long diagonals must also contain the digits 1 through 9 exactly once.
If you already enjoy classic Sudoku and want a cleaner rule twist without changing the rest of the interface, this is the fastest way to practice diagonal logic on the original board.
The row, column, and 3×3 box rules still apply. The only difference is that the main diagonal and the anti-diagonal are now full houses too, which makes the center area especially important.
Any cell on a diagonal belongs to one more constraint group than a normal Sudoku cell. The center cell belongs to both diagonals, so it often becomes a key anchor for the whole puzzle.
This page highlights both diagonals directly on the board so you can see the extra rule without changing the rest of the original UI.
A move may look fine by row, column, and box, but still be illegal because it duplicates a digit on one of the diagonals. On this page, those diagonal conflicts are surfaced on the board itself.
You can still use reset, import, export, and solver mode. On the X-Sudoku route, imported and solved boards are validated against the diagonal rule too.
X-Sudoku rewards the same steady scanning habits as classic Sudoku, but it gives you two more structured lines to exploit when a puzzle stalls.
New to diagonal Sudoku? Read the X-Sudoku rules guide to learn how the two diagonal constraints work. For experienced players, our advanced X-Sudoku techniques cover diagonal X-Wing patterns and diagonal-box interactions.