Sudoku generator
A grid with one solution and one only, at the difficulty you ask for.
- Given numbers
- 31
- Hardest step needed
- Naked pair
Print this one
One PDF: the sheet on the first page, the answer key on the second.
One PDF: the sheet, and the answer key on the page after it.
How it works
Every grid here is dug out of a complete solution one cell at a time, and after each cell the puzzle is re-solved to make sure exactly one answer is still possible. A sudoku with two answers is not a hard sudoku, it is a broken one.
- 1Pick a difficulty. Easy needs nothing but singles; expert needs a technique with a name.
- 2A grid is generated in your browser, checked, and graded by the hardest step it really needs.
- 3Download the sheet, with the finished grid on the page after it.
Sudoku generator
What makes a sudoku hard?
Not the number of given digits, which is what most generators go by. What matters is the hardest technique you have to use: an easy grid falls to single candidates, a hard one needs an X-wing. Each grid here says which one it needs.
Can a grid have more than one answer?
Not one that comes out of here. The check runs after every digit removed, and it stops counting at two: if a second answer turns up, the digit goes back.
How few numbers can a sudoku start with?
Seventeen. That is proven, not estimated: an exhaustive search showed no sixteen-clue grid with a single answer exists. Expert grids here sit in the low twenties.