Diagonal Sudoku
An alternate name for Sudoku X — the 9×9 Sudoku variant where both diagonals carry the same digit-uniqueness rule as rows, columns, and boxes.
Diagonal Sudoku is the same puzzle as Sudoku X. Both names refer to a 9×9 Sudoku variant where, in addition to the standard row, column, and 3×3 box uniqueness rules, each of the two diagonals must contain every digit 1 through 9 exactly once.
The two names exist for historical and SEO reasons rather than mechanical ones. Diagonal Sudoku is the more literal description and the older name in continental European puzzle communities; Sudoku X is the name that took hold in English-language puzzle publishing because the diagonal cells visibly trace an X across the grid. Neither is more correct than the other.
Which name to use
In most contexts, the two names are interchangeable. Search engines treat them as synonyms. Puzzle constructors typically pick one based on house style. On Sudoku Mountain we use Sudoku X as the primary label on play surfaces (because it's shorter and surfaces well in short headlines) and acknowledge Diagonal Sudoku throughout the educational content (because it's the higher-volume search phrase in most English-speaking markets).
If you're looking for the rule set or how the variant differs from classic Sudoku, see the main Sudoku X entry. If you'd like a hands-on walk through your first puzzle, Sudoku X for beginners is the right starting point.
See also
- Sudoku X— A Sudoku variant where both diagonals must also contain each digit 1-9 exactly once. Also known as Diagonal Sudoku. Classic Sudoku plus two new units.
- Diagonal constraint— The extra rule that defines Sudoku X (Diagonal Sudoku): each of the two diagonals must contain every digit 1-9 exactly once, just like a row or column.
- Forced cell on the diagonal— A Sudoku X (Diagonal Sudoku) deduction: a cell on the diagonal whose digit is forced by row, column, box, and diagonal together — no three of them suffice.
- Diagonal pair— A naked pair where both cells lie on the same diagonal of a Sudoku X. Eliminates the two pair digits from every other cell on that diagonal.
Read more
- The rules of Sudoku X
Sudoku X — also called Diagonal Sudoku — is classic Sudoku with one extra rule: both diagonals must also contain each digit 1–9 exactly once.
- Meet Sudoku X
An introduction to Sudoku X (a.k.a. Diagonal Sudoku) — what the diagonal rule adds, why classic solvers tend to enjoy it, and how to know if it's for you.