Hard sudoku
Free, with notes, hints and undo
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About this level
Hard puzzles start with 24 to 31 numbers and can't be finished with single-option moves alone. You'll need pairs: two squares or two lines that lock a number in place.
The move you'll use most is the pointing pair. If every possible spot for a 4 inside one box sits on the same row, then that row's 4 must be in that box, so you can cross 4 off the rest of the row. Our strategies page walks through it with a picture.
Notes stop being optional at this level. Fill in candidates for a box or a row, look for two squares that share the same two options, and clear those two numbers from the rest of the group. That's a naked pair.
Of 200 hard puzzles from our generator, 197 needed a pointing pair or box-line move, 49 needed a naked pair and 16 a hidden pair. None needed guessing.
New to the game? Start with how to play sudoku. Want the same puzzle as everyone else today? Try the daily sudoku.
More sudoku
- Daily sudokuA new easy, medium and hard puzzle every day, the same for everyone.
- Easy sudokuPlenty of clues. Every move can be found by looking for single options.
- Medium sudokuFewer clues, same simple logic. A good daily level.
- Expert sudokuNeeds X-wings or triples. Still no guessing.
- Printable sudokuLarge-print sheets for pencil and paper, with answers.
- How to play sudokuThe rules, a first walk-through and the controls on this site.
- Sudoku strategiesFrom hidden singles to X-wings, with examples.