Sudoku Solver
Type any 9×9 sudoku into the grid and solve it instantly, with duplicate checking as you type.
Type the digits you know, then press Solve. Blank cells stay empty.
- Clues
- 0
- Empty cells
- 81
- Solve time
- —
Tip: use the arrow keys to move around the grid, Backspace to clear a cell. Solved digits appear in a lighter colour so you can tell them from your own clues.
How it works
Type your puzzle into the 9×9 grid — one digit per cell, blanks left empty — and press Solve. The solver uses classic depth-first backtracking with the minimum-remaining-values heuristic: it always fills the cell with the fewest legal candidates first, which solves even "hardest ever" newspaper puzzles in a few milliseconds. Every standard sudoku rule is enforced — each digit 1–9 exactly once per row, per column and per 3×3 box.
As you type, the grid checks itself: any digit that repeats in a row, column or box is highlighted immediately so you can fix a typo before solving. The solver also searches for a second solution, so it can tell you whether your puzzle is a proper sudoku (exactly one answer), ambiguous (several answers) or impossible. All of it runs as JavaScript in your own browser — the puzzle is never uploaded anywhere.
Frequently asked questions
How does this sudoku solver work?
It uses depth-first backtracking with the minimum-remaining-values heuristic: the solver repeatedly fills the empty cell that has the fewest legal candidates, backing up whenever a cell runs out of options. That ordering makes even the notoriously hard puzzles finish in a few milliseconds, entirely in your browser.
Can a sudoku puzzle have more than one solution?
Yes. A proper sudoku has exactly one solution, but a grid with too few or badly chosen clues can have many — no puzzle with fewer than 17 clues can be unique. This solver searches for a second answer as well, so it tells you whether your puzzle is unique, ambiguous, or impossible.
Is my puzzle uploaded anywhere?
No. The whole solver is JavaScript running on your device, so the digits you type never leave your browser. There is no account, no ads and no server round-trip — you can even use it with your connection switched off once the page has loaded.