Sudoku Solver and Generator
Enter a Sudoku grid to solve it instantly, or generate a fresh puzzle by difficulty. The solver finds the unique answer, flags clashing clues and shows the candidates for any empty cell.
How to solve a Sudoku
- Type the known digits into the grid, leaving unknown cells blank.
- Press Solve to fill in the unique solution, or Generate to build a new puzzle.
- Copy the solution string or clear the board to start again.
Examples
Solve a classic puzzle
53..7....6..195....98....6.8...6...34..8.3..17...2...6.6....28....419..5....8..79
534678912672195348198342567859761423426853791713924856961537284287419635345286179
Frequently asked questions
Does every Sudoku have one answer?
A well-formed puzzle has exactly one solution. The solver tells you when a grid is unsolvable or has more than one solution, so you can spot a bad puzzle.
How do I type a puzzle?
Click a cell and press 1 to 9, or paste an 81-character line using digits with a dot or 0 for blanks. Spaces and grid borders are ignored.
How does the solver work?
It uses constraint-based backtracking with the minimum-remaining-values heuristic, the same logic expert humans use, so it solves even the hardest grids in milliseconds.
Are the generated puzzles unique?
Yes. Each generated puzzle is checked to have exactly one solution, and harder difficulties simply leave fewer starting clues.
Is my puzzle uploaded anywhere?
No. Solving and generating run entirely in your browser, so nothing is sent to a server.
Learn more
- Sudoku solving techniques, from easy to expert
Learn the logic behind solving Sudoku: naked singles, hidden singles, locked candidates and when backtracking takes over.
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