How to Play Diagonal Sudoku

Both main diagonals must also contain 1–9

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The Rules

Standard Sudoku rules apply: fill every row, column, and 3×3 box with the digits 1–9, each appearing exactly once.

In Diagonal Sudoku, the standard 9×9 rules apply — but with one powerful extra constraint: both main diagonals (top-left to bottom-right, and top-right to bottom-left) must each contain every digit from 1 to 9 exactly once. This extra constraint typically makes the puzzle easier to solve since diagonals act as two extra units for elimination.

At a Glance

22–28
Typical givens
Extra Regions
Constraint type
~4m
Easy solve time
~10m
Medium solve time

How to Solve Diagonal Sudoku

Beginner
Diagonal as a Unit
Treat each diagonal exactly like a row or column — every digit 1–9 appears exactly once. Standard scanning and counting apply.
Intermediate
Diagonal–Box Interaction
When a digit on a diagonal is confined to one box segment, eliminate it from the rest of that box.
Intermediate
Diagonal Naked Pairs
If two cells on a diagonal share the same two candidates, eliminate those values from all other diagonal cells.
Advanced
Three-Unit Intersection
A cell on the main diagonal also belongs to a row, column, and box — four constraint units simultaneously — maximising elimination power.
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Common Questions

Which diagonals are constrained? ▾

Both the main diagonal (top-left to bottom-right) and the anti-diagonal (top-right to bottom-left) must each contain 1–9 exactly once.

Are diagonal puzzles easier than classic? ▾

Often yes — the extra units provide more candidates to eliminate, typically reducing advanced technique requirements.

Does the diagonal constraint always create a valid puzzle? ▾

Yes — our generator ensures a unique solution exists with the diagonal rules in place.

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