| 3 | 8 | |||||||
| 9 | 7 | 8 | 3 | |||||
| 8 | 1 | 2 | ||||||
| 7 | 5 | 6 | ||||||
| 6 | 8 | 7 | 9 | |||||
| 2 | 3 | 1 | ||||||
| 9 | 3 | 5 | ||||||
| 5 | 8 | 4 | 6 | |||||
| 2 | 7 |
Hard Sudoku
Fill the grid so every row, every column and every three-by-three box contains each digit from 1 to 9 exactly once. Somewhere in this grid the singles run out and you will need a fish or a wing: an X-Wing across two lines, or an XY-Wing pincering a digit from two sides.
What makes this puzzle Hard?
This grid has 28 clues. Solving it without guessing requires at most a X-Wing. We rate difficulty by the hardest logical technique a puzzle actually needs — not by how many digits we removed. Two puzzles with the same number of clues can be worlds apart, which is why clue count alone makes such a poor difficulty label.
Every technique this engine uses is documented, each with a worked example from a real puzzle: see solving techniques. Prefer paper? Printable Hard sudoku as a free PDF.
Other difficulties
- Very Easy sudoku — pure scanning, nothing but singles
- Easy sudoku — adds locked candidates and pairs
- Medium sudoku — adds triples and quads, and fewer clues
- Hard sudoku — needs an X-Wing or an XY-Wing
- Expert sudoku — needs colouring, a Swordfish or an XYZ-Wing
- Master sudoku — needs an XY-chain