Sudoku Solver & Generator
Free online Sudoku solver with puzzle generator. Works entirely in your browser.
Loading tool...
What is Sudoku Solver & Generator?
The Sudoku Solver generates and solves standard 9x9 Sudoku puzzles entirely in your browser. Type clues into the grid or paste an 81-character puzzle string, and a backtracking solver with a minimum-remaining-values heuristic returns the complete solution while verifying whether it is the only one. The generator creates fresh puzzles with a guaranteed unique solution across Easy, Medium, and Hard difficulty levels.
Key Benefits
- Solves any well-formed puzzle in milliseconds with a MRV backtracking search
- Distinguishes unsolvable, unique, and multi-solution puzzles instead of guessing
- Generates printable puzzles with exactly one solution at three difficulty levels
- Fully private and offline-capable — no upload, no account, no limits
Common Use Cases
- •Finishing a newspaper or app puzzle you are stuck on without spoilers ahead of your row
- •Checking a hand-crafted puzzle before publishing it to confirm it has a unique solution
- •Generating fresh printable boards for a classroom, flight, or puzzle night
- •Converting puzzle strings between solvers during friendly competitions
How to Use the Sudoku Solver
- Enter the clues: Type the given digits into the grid, or paste an 81-character puzzle string into the import box and click Load String.
- Solve the puzzle: Click Solve Puzzle. The solver checks conflicts, finds a complete solution, and tells you whether it is unique.
- Generate a new puzzle: Switch to the Generate tab, pick Easy, Medium, or Hard, and click Generate Puzzle for a fresh board with exactly one solution.
- Copy or share: Click Copy String to export the 81-character puzzle string, or copy the solved grid for printing.
Key Features
- Backtracking solver with MRV heuristic solves hard grids in milliseconds
- Solution counter reports 0, 1, or multiple valid solutions
- Generator with Easy, Medium, and Hard levels, always a unique solution
- Import and export 81-character puzzle strings
- Keyboard navigation with arrow keys across the grid
Frequently Asked Questions
Does the solver check whether a puzzle has a unique solution?
Yes. The solver searches for up to two solutions: zero means the clues conflict, one means the puzzle is well-formed, and two means multiple solutions exist, which strict Sudoku rules disallow.
How does the generator create puzzles?
It first fills a complete valid grid with randomized backtracking, then removes clues one by one in random order, keeping only removals that still leave exactly one solution.
What is the puzzle string format?
A single line of 81 characters: digits 1-9 for clues and 0, period, underscore, or hyphen for empty cells. This format is compatible with most online Sudoku solvers.
Are my puzzles uploaded anywhere?
No. All solving and generation happens locally in your browser with plain JavaScript, so the tool keeps working even offline once the page has loaded.