✖️ How to play Sudoku X (Diagonal Sudoku)
By Miguel Arechaga
Diagonal Sudoku, also known as Sudoku X, is one of the most popular variants of classic sudoku. It adds one extra rule that's simple to understand but completely changes how you reason: the board's two main diagonals must also contain 1 to 9 without repeats. Here are the rules and tips to master it.
What is Sudoku X?
It's a 9x9 sudoku variant where, on top of the usual rules, a restriction is added on the two main diagonals (the cells running corner to corner, usually shaded). It's called Sudoku X because those two diagonals draw an X across the board.
Rules and how to play step by step
- The sudoku rules apply: 1 to 9 without repeats in each row, column and 3x3 box.
- In addition, each of the two main diagonals must contain 1 to 9 without repeats.
- You start with some clue cells and fill in the rest with logic.
- Every puzzle has a unique solution, reachable without guessing.
Tips to solve Sudoku X
- Start with the diagonals: they're the best source of extra clues. The center cell belongs to both diagonals at once, so it's often deduced early.
- Double elimination: a diagonal cell gets restrictions from its row, its column, its box and its diagonal. There are usually fewer candidates than it seems.
- When a diagonal has almost all its numbers, apply the same reasoning as with a row: whatever's missing is missing.
- Combine the X rule with the classic techniques: each number placed on a diagonal opens new deductions in two directions.
How it differs from regular sudoku
Compared to classic sudoku, Sudoku X adds two more "regions" (the diagonals), which gives more starting clues but requires watching more restrictions at once. If you enjoy variants, you'll also enjoy Killer Sudoku. It's a great way to refresh the classic sudoku with a new challenge.
