Check whether a sudoku puzzle is solvable and unique
Stuck on a puzzle — or building one? The solver returns the solution and counts whether it's the only one.
Tools used in this guide
The job
Two questions matter: does this grid have a solution, and is it the only one? A newspaper puzzle should be unique; a half-empty grid almost never is.
Givens in, answer out
Type the clues into the grid or paste 81 digits (0 or . for blanks). Solve fills the grid and reports the count found — the tool checks up to 2 solutions, enough to separate unique from ambiguous.
- A contradiction in the givens (two 7s in a box) is caught before solving.
- 'Multiple solutions' doesn't mean the puzzle is broken for casual play — it means guessing was required.
For constructors
Test each draft: remove a given, re-solve, and watch for the unique→multiple flip. Puzzles with few givens (under ~25) are rarely unique — classic minimum-clue puzzles sit at 17.