Sudoku X Strategy: 5 Techniques
Everything you know from sudoku still works. The diagonals simply give you two more units to run the same techniques on. New here? Read the rules first.
1. Count the diagonals as units
A hidden single is a digit with only one place left in a unit. Check the diagonals for hidden singles exactly as you check rows and boxes: they're often the easiest ones on the grid.
2. Start at the centre
The centre cell belongs to five units. Whatever digits are already on both diagonals, its row, its column and the middle box are all ruled out at once.
3. Diagonal and box overlaps
Each diagonal crosses three cells of a corner box and three of the centre box. If a digit on the diagonal must be in those three cells, it can't be elsewhere in the box, and the other way round.
4. Diagonals break symmetry
Plain sudoku gets stuck on patterns where two cells could swap. If one of those cells is on a diagonal, the diagonal usually decides which digit goes where.
5. Keep notes on the diagonal cells
Eighteen cells carry the extra rule (the centre counts for both). Writing candidates in them first pays off, because they're the cells where the most eliminations arrive.
Frequently asked questions
Where should I start a Sudoku X?
At the centre cell: it sits in a row, a column, a box and both diagonals, so it has the most constraints of any cell and is often the first to fall.
Last updated 2026-10-20