sudokly
9×9 · Medium to expert

Diagonal Sudoku (X-Sudoku)

Classic sudoku plus a constraint on both main diagonals.

Medium00:00✕ 0
About diagonal

What diagonal sudoku (x-sudoku) feels like.

Diagonal sudoku. sometimes called X-sudoku. adds two extra constraints to classic sudoku: both the top-left-to-bottom-right and top-right-to-bottom-left diagonals must each contain digits 1 through 9 exactly once. Those extra constraints make for tighter logic and fewer starting clues.

Rules

  1. Standard 9×9 sudoku rules apply.
  2. The main diagonal (top-left to bottom-right) contains each digit 1–9 exactly once.
  3. The anti-diagonal (top-right to bottom-left) contains each digit 1–9 exactly once.
Key rule
Both main diagonals also contain 1–9
Difficulty range
Medium to expert
Tips
  • Track diagonals as you would a row or column. they're extra elimination groups.
  • The centre cell (r5, c5) sits on both diagonals, so digits there cascade widely.
  • When stuck, check whether either diagonal is missing only one or two digits.

Diagonal Sudoku (X-Sudoku) FAQ

What is X-sudoku?

X-sudoku is another name for diagonal sudoku: a 9×9 sudoku with the added constraint that both main diagonals also contain digits 1–9 exactly once.

Is diagonal sudoku harder than classic?

Slightly harder for a given clue count, but easier to solve at a fixed difficulty rating. the extra constraints provide more elimination paths.

Do both diagonals always have the constraint?

In standard diagonal sudoku, yes. Some variants only constrain one diagonal. Sudokly uses both.

Can I solve diagonal sudoku with classic techniques?

Mostly. The extra diagonals mean hidden singles often appear there first. always scan them.

Are diagonal puzzles unique?

Yes. Uniqueness is verified during generation.