What is Diagonal Sudoku?
Diagonal Sudoku, often called X-Sudoku, is one of the gentlest Sudoku variants to learn: it keeps every rule of classic 9×9 Sudoku and adds exactly one more. Alongside each row, column and 3×3 box, both main diagonals — top-left to bottom-right, and top-right to bottom-left — must also contain the digits 1 through 9 exactly once.
How solving changes
- Extra elimination power: a digit already placed on a diagonal can't appear anywhere else on that diagonal, even outside its row, column or box — a new source of eliminations classic Sudoku doesn't give you.
- Diagonal cells resolve first: because they carry two constraints at once (their diagonal, plus row/column/box), diagonal cells often become naked singles sooner than the rest of the grid.
- Same core techniques still apply: naked singles, hidden singles, pairs and pointing pairs all work exactly as they do in classic Sudoku — you're just solving with one extra rule in play.
Every Diagonal Sudoku puzzle on this page is freshly generated and checked to have exactly one valid solution under both the classic rules and the diagonal rule — never a guess required.
