ADVANCED VARIANT · DIAGONAL
Diagonal Sudoku Online
Diagonal Sudoku, also called Sudoku X, keeps every classic rule and adds both long corner-to-corner diagonals as extra regions containing digits 1 through 9 once.
Diagonal rules
Rows, columns and 3×3 boxes remain unchanged. The two highlighted main diagonals must each contain every digit exactly once.
Watch the center
The center cell belongs to both diagonals as well as its row, column and box, making it one of the most constrained cells.
Integrity validation
Sudoku Genius uses a diagonal-aware candidate engine and solver to validate the deterministic puzzle and its unique solution.
Resume safely
Diagonal identity is stored with the puzzle, preventing classic and diagonal save states from being mixed.