Is Diagonal Sudoku harder than classic Sudoku?
It can feel different at first, but the extra diagonal rule also gives more clues to reason with.
Diagonal Rules
Diagonal Sudoku Rules
Diagonal Sudoku follows the classic 9x9 rules and adds one visual rule: each long diagonal also needs the numbers 1 through 9 exactly once.
Rule profile
- Classic rules
- Every row, column, and 3x3 box still uses 1 through 9 once.
- Extra rule
- The two corner-to-corner diagonals also use 1 through 9 once.
- Best start
- Use Easy before Medium if the diagonal rule is new.
- Senior fit
- The extra rule is visual, not math-heavy or symbol-heavy.
The fourth check
Classic Sudoku asks you to check rows, columns, and boxes. Diagonal Sudoku adds a fourth check only for the two long diagonals.
A number can go on a diagonal square only if it does not already appear in that row, column, box, or the same diagonal.
- Main diagonal: top-left to bottom-right.
- Second diagonal: top-right to bottom-left.
- The center square belongs to both diagonals.
How to read the board
Large Sudoku lightly highlights the diagonal squares so the extra rule is visible without covering the large numbers.
The rule does not change the size of the board, so classic 9x9 skills still transfer directly.
Practical Questions
Does the center square count twice?
The center square sits on both diagonals, so it must fit both diagonal checks as well as its row, column, and box.