Sudoku X — play the diagonal variant free online

Classic sudoku with one elegant twist: both main diagonals must also contain the digits 1–9. 400,000 puzzles across four difficulties, every one verified to have exactly one solution.

How Sudoku X works

All the normal rules apply — every row, column and 3×3 box holds 1–9 exactly once. Sudoku X adds two more units: the two shaded corner-to-corner diagonals must each contain 1–9 as well. The centre cell is special: it sits on both diagonals, making it the most constrained cell on the grid and often the best place to start.

Why solvers love the X

• The diagonals cut both ways. On easier puzzles they're a gift — two extra units to scan for singles. On Expert, they're the only information you have, and 22 givens is all you get.
• Familiar but fresh. Every classic technique still works; the diagonals just weave new elimination chains through the middle of the grid that classic sudoku never has.
• The centre-cell trick. Whatever digit occupies r5c5 is locked out of both entire diagonals — 16 other cells constrained by one placement.

Four difficulties

• X Easy — 38 givens. The diagonals do half the work for you.
• X Medium — 31 givens. The balanced experience.
• X Hard — 26 givens. Now they're working against you.
• X Expert — 22 givens. The diagonals are all you've got.

Puzzle numbers are permanent and shareable, progress saves automatically in your browser, every puzzle prints as a clean grid with the diagonals shaded, and there's dark mode for the late sessions.

New to sudoku entirely?

Start with classic sudoku — the Coward's mode teaches you the game one obvious step at a time. And when diagonal sudoku stops being enough of a fight, killer sudoku is the site's main event.