What are the X Sudoku rules?

Keep the usual 9×9 Sudoku rules and add both main diagonals. The shaded line from top left to bottom right is diagonal 1; the line from top right to bottom left is diagonal 2. Each must hold 1 to 9 exactly once. The centre square belongs to both.

How does the diagonal solver find contradictions?

It checks duplicate digits in rows, columns and boxes, then in both diagonals. Even if no pair clashes, it searches for a completion satisfying all those units. A classic solution that repeats a diagonal digit is rejected while X Sudoku is selected.

Can I get hints for diagonal Sudoku?

Choose Step to fill one proved square. Candidate checks and hidden singles include the diagonal rules. A move requiring exhaustive backtracking is identified as a search deduction.

Is the example a uniquely solvable X Sudoku?

Yes. Its 18 givens have exactly one completion when both diagonal rules are applied. Without those diagonal restrictions the same givens allow more than one classic completion.

Does this support Killer or jigsaw Sudoku?

This preset is for a 9×9 grid with ordinary 3×3 boxes and both main diagonals. It has no cage totals, irregular regions or overlapping boards.

X Sudoku Solver

Solve a diagonal Sudoku whose rows, columns, 3×3 boxes and two main diagonals each contain 1 to 9. A new draft opens with X Sudoku selected; a saved draft restores its grid and rule choice. Enter your puzzle or try the 18-given example below the controls.

Selected: R1C1

Empty grid0 givens

Both shaded main diagonals must each contain 1 to 9. Diagonal 1 runs from top left; diagonal 2 runs from top right.

Type the givens into the grid, or paste 81 characters, then press Solve. Arrow keys move, a digit types, backspace clears.

Entry

Givens

Solutions

not solved yet

Tap a square, then a number below the grid, or use the keyboard. Arrow keys move, digits enter, backspace erases and Enter runs the selected action. Your entries are white; solver entries are coloured. Editing or changing rules clears the solver entries. Contradicting squares turn red. Fill every empty square at once, and say how many solutions the grid has.

An X Sudoku grid and what comes back

An X Sudoku puzzle18 givens, one solution with both diagonals
solved, one solution

Counted, not guessed. One answer means every digit is forced by the givens and selected rules. More than one means the displayed completion is one possible answer. Step labels any exhaustive search deduction separately from a naked or hidden single.

Accuracy. Exact: the answer satisfies every row, column and box, or the tool says the puzzle has none. It counts solutions as it searches, so it can tell you when a grid has more than one, and it cannot know which of those the puzzle author intended. Nothing is uploaded: the grid, the search and the counting all run in this tab, so it works with no connection once the page has loaded.

Common questions

What are the X Sudoku rules?: Keep the usual 9×9 Sudoku rules and add both main diagonals. The shaded line from top left to bottom right is diagonal 1; the line from top right to bottom left is diagonal 2. Each must hold 1 to 9 exactly once. The centre square belongs to both.
How does the diagonal solver find contradictions?: It checks duplicate digits in rows, columns and boxes, then in both diagonals. Even if no pair clashes, it searches for a completion satisfying all those units. A classic solution that repeats a diagonal digit is rejected while X Sudoku is selected.
Can I get hints for diagonal Sudoku?: Choose Step to fill one proved square. Candidate checks and hidden singles include the diagonal rules. A move requiring exhaustive backtracking is identified as a search deduction.
Is the example a uniquely solvable X Sudoku?: Yes. Its 18 givens have exactly one completion when both diagonal rules are applied. Without those diagonal restrictions the same givens allow more than one classic completion.
Does this support Killer or jigsaw Sudoku?: This preset is for a 9×9 grid with ordinary 3×3 boxes and both main diagonals. It has no cage totals, irregular regions or overlapping boards.

Exact: the answer satisfies every row, column and box, or the tool says the puzzle has none. It counts solutions as it searches, so it can tell you when a grid has more than one, and it cannot know which of those the puzzle author intended.