Sudoku Solver
Type in a puzzle or paste it as 81 digits, then solve it in one click or one step at a time. Each step names the technique that places the digit, so you can see why it goes there, not just what goes there.
How the solver works
First the solver checks your clues. It flags any digit that repeats in a row, column, or box, and it counts solutions so you know whether the puzzle is valid. A proper sudoku has exactly one.
Then it solves the way a person would. It keeps a full set of pencil marks, places a digit whenever a single is available, and otherwise looks for an elimination, from pointing pairs up to the Swordfish, that opens up the next placement.
Some very hard puzzles need techniques beyond that list, such as chains. When logic runs out, the solver finishes the remaining cells by trial and error and tells you exactly which cells those were.
Everything runs in your browser. Your puzzle is never sent to a server.
Techniques it uses
The solver tries these in order, easiest first, the same way a person would.
- Naked single: A cell where only one digit is still possible.
- Hidden single: A digit that fits in only one cell of a row, column, or box.
- Pointing pairs and box/line reduction: When a digit is locked to one line inside a box (or one box inside a line), it can be crossed off elsewhere.
- Naked pairs and triples: Two or three cells that share the same two or three candidates claim those digits.
- Hidden pairs: Two digits that can only go in the same two cells of a unit.
- X-Wing: A digit locked to the same two columns in two rows, or the same two rows in two columns.
- Swordfish: The three-line version of the X-Wing.
FAQ
How do I enter a puzzle?
Click a cell and type a digit, using the arrow keys to move. Backspace, Delete, or 0 clears a cell. You can also paste the whole puzzle as 81 characters, reading left to right and top to bottom, with 0 or a dot for each blank.
Can it solve any sudoku?
It finds the answer to any valid 9x9 sudoku, usually in a few milliseconds. Most newspaper and app puzzles solve with logic alone. For the very hardest puzzles, the last few cells are filled by trial and error, and the solver says so.
Why does it say my puzzle has more than one solution?
A real sudoku has exactly one answer. If a clue is missing or was copied wrong, several grids can fit, and there is no single answer to show. Check the clues against the original.
Why does it need at least 17 clues?
It has been proven that no 9x9 sudoku with fewer than 17 clues has a unique solution. With 16 or fewer there is always more than one answer.
Can I play the puzzle instead of just seeing the answer?
Yes. Once the puzzle is valid, choose Play this puzzle to open it in the full game with notes, hints, undo, and a timer.
Is the solver free?
Yes. It is free, has no ads, and does not need an account.
Rather solve it yourself?
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