About Sudoku X
Sudoku X, also called diagonal sudoku, adds one rule to the classic: the two long diagonals must each contain every digit once. It opens up new deductions — cells on the diagonals are constrained by an extra unit — and every puzzle here still has exactly one solution.
How to play
Fill the grid so every row, column and 3×3 box contains 1–9 exactly once — and so do the two shaded diagonals. The extra rule gives you more to work with, so fewer starting digits are needed.
Tips and strategies
- Start with the centre cell: it lies on both diagonals, its row, column and box.
- Treat each diagonal as a tenth and eleventh unit when scanning for missing digits.
- Diagonal cells in the corner boxes often resolve early — check them first.
Sudoku X strategy guide
Start with the diagonals. Each one crosses the centre and three boxes, so a digit missing from a diagonal often has only one free cell left on it.
The centre cell belongs to both diagonals, the middle row, the middle column and the centre box — five groups at once — so it is often one of the first cells you can pin down.
Use the diagonals for elimination too. A digit placed on a diagonal removes that digit from every other cell of the diagonal, which can finish a box that row and column scans alone could not.
Frequently asked questions
How is Sudoku X different from classic Sudoku?
Both long diagonals of the 9×9 grid must also contain the digits 1–9 exactly once, on top of the usual rows, columns and 3×3 boxes. The diagonal cells are shaded so you can see them.
How many clues does each difficulty give?
About 38 on Easy, 31 on Medium and 26 on Hard. The extra diagonal rule lets Sudoku X stay unique with fewer clues than a classic Sudoku.
Does every Sudoku X have exactly one solution?
Yes. Clues are removed only while a solver, applying the diagonal rule too, still finds exactly one solution.
Is Sudoku X free to play?
Yes. Every game on Puzzimo is completely free and runs in your browser on desktop, tablet and phone — no download or installation.
Do I need an account?
No. You can play instantly as a guest and still appear on the leaderboards. Sign in with Google, Discord or LINE to keep your scores on every device.
How does the daily Sudoku X challenge work?
Every day at 00:00 UTC everyone gets the same new puzzle. Only your first finish of the day counts on the leaderboard.
How are leaderboard results verified?
Our servers replay every move of your game and measure the time themselves, so leaderboard results can't be faked.