Paused
So there are four kinds of group to keep in mind:
- every row
- every column
- every 3 by 3 box
- the two diagonals, top left to bottom right and top right to bottom left
The puzzle is also called Diagonal Sudoku or X-Sudoku. Every puzzle here has exactly one answer.
How to play
Start in the middle
The centre square is on both diagonals, so five groups limit what it can be: its row, its column, its box and two diagonals. It is often the first square you can solve. The four corners are the next best spots, because each sits on one diagonal plus a row, column and box.
Treat the diagonals as two extra rows
When you scan for a number, check the diagonals the same way you check a row. If a diagonal already has a 6, no other shaded square on that diagonal can be 6. Selecting a diagonal square shades the whole diagonal, so you can see this at a glance.
Watch boxes 1, 5 and 9
One diagonal runs through the top left, centre and bottom right boxes. The other runs through the top right, centre and bottom left. The diagonal squares in these boxes are tightly limited, and solving them often unlocks the rest of the box.
Why Sudoku X can start with fewer numbers
Each rule adds information. Because the diagonals also have to hold 1 to 9, a Sudoku X puzzle needs fewer starting numbers to have only one answer. Our Easy level starts with about 36 numbers, and Expert with about 22.
The four levels
| Easy | About 36 starting numbers. A good first Sudoku X. |
|---|---|
| Medium | About 30. The diagonals start to matter for most moves. |
| Hard | About 26. Notes needed in several boxes. |
| Expert | About 22. You will need pairs and pointing pairs along the diagonals. |
Questions people ask
What is Sudoku X?
Sudoku X is classic Sudoku with one extra rule: the two long diagonals, from corner to corner, must each hold the numbers 1 to 9 once. The diagonal squares are shaded so you can see them.
Is Sudoku X the same as Diagonal Sudoku?
Yes. It is also called X-Sudoku or Sudoku Diagonal. Some books call it Sudoku X because the two diagonals form a large X across the grid.
Is Sudoku X harder than normal Sudoku?
Not necessarily. The extra rule gives you more information, so a Sudoku X puzzle can start with fewer numbers and still have one answer. At the same level it plays about as hard as a classic puzzle, but you have to remember to check the diagonals.
Which square should I start with?
The centre square sits on both diagonals as well as its own row, column and box, so it is limited by five groups at once. The four corners are also on a diagonal and are often quick to fill.
More Sudoku games
Classic Sudoku
The everyday game, from Easy to Extreme.
Daily Sudoku
Four puzzles a day, the same for everyone.
Killer Sudoku
Few or no numbers to start. Cages tell you their totals.
Jigsaw Sudoku
The boxes are wiggly pieces instead of squares.
Mini Sudoku
A quick game with the numbers 1 to 6.
Sudoku for Kids
Four numbers, big squares, no game over.
Sudoku 16 × 16
The numbers 1 to 16 on a 256 square grid.
Christmas Sudoku
Classic Sudoku dressed for the holidays, to play or print.
All games and tools
Every game on the site, the difficulty pages, printable puzzles and the solver.