Hard Sudoku — play challenging puzzles online

Hard Sudoku separates casual players from serious solvers. With only 24 to 36 numbers on the grid, every move requires careful analysis and there are often no obvious next steps.

At this level, you need advanced techniques: X-Wing lets you eliminate candidates by finding rectangular patterns across rows and columns. Box/line reduction helps narrow down possibilities within blocks. Swordfish — an extension of X-Wing across three rows — becomes useful for the trickiest puzzles.

Hard puzzles demand patience and systematic thinking. The satisfaction of cracking a hard Sudoku when you finally break through is unmatched. This is where the rating system truly comes alive — hard puzzles earn you a 0.5x points multiplier.

On OnSudoku, 9,182 hard puzzles have been solved, with an average time of 522 seconds.

Mastered hard puzzles? The Expert level is the ultimate test, designed for players who want the toughest challenge possible.