Expert Sudoku X Online
Free 9×9 Sudoku X at the hardest tier — sparse givens, diagonal constraint, extreme technique.
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All-TimeExpert Sudoku X is the hardest tier we generate. With 20–22 givens and the diagonal constraint forcing the deepest deductions, almost every move comes from technique rather than scanning — swordfish on a diagonal, Unique Rectangle straddling both diagonals, XY-Wing chains that exploit the diagonal intersection at the centre cell. Sessions take real time; 30–60 minutes is normal, longer for the toughest grids. Sudoku247Online's diagonal-aware solver verifies every Expert puzzle has a single legal solution before it ships — no guesswork required, just patient deduction along three axes instead of two.