CageDokuSudoku X (Diagonal Sudoku) Rules and Tips
By Andrew Boyko, developer of CageDoku · Updated
Sudoku X, also called Diagonal Sudoku, adds one visual rule to classic Sudoku: both main diagonals must also contain every digit from 1 to 9 exactly once.
The rules
- Every row, column and 3×3 box contains 1 to 9 once.
- Each of the two main diagonals contains 1 to 9 once.
The centre cell
The centre cell belongs to both diagonals, so its digit cannot appear anywhere else on either diagonal. It sees 16 diagonal cells plus its row, column and box.
Diagonal and box interaction
Each diagonal passes through three boxes (two corner boxes and the centre box), three cells in each. The centre box contains five diagonal cells. If a digit’s only candidates in a corner box lie on the diagonal, the diagonal “uses” that digit there and the digit is excluded from the rest of the diagonal.
Where to start
Sudoku X is one of the gentlest variants: the extra rule only adds eliminations. If you know classic Sudoku, it is a fun first step into variants.
Practice
Try a Diagonal puzzle in your browser; hints highlight the diagonals when they matter.
Frequently asked questions
How many cells are on the diagonals?
Each diagonal has nine cells; together the two diagonals cover 17 cells because they share the centre.
Practice it in CageDoku
Free, ad-free Killer Sudoku and seven more variants. Hints name the technique and highlight the cells, so you learn why a digit goes where it goes.