How does it work?
Enter the numbers your puzzle already has, then press Solve Sudoku. Tap a cell and pick a digit from the pad, or use the keyboard: arrow keys to move, 1–9 to place, Backspace to erase. You can also paste a whole puzzle as 81 characters.
Introducing the Sudoku solver
It is for the grid you have been staring at for twenty minutes. Type it in and you get the answer immediately — and, unlike a friend looking over your shoulder, it also tells you when the grid you typed cannot be solved at all, which is usually a copying mistake rather than a hard puzzle.
What you get
- An answer to any valid grid, in a few milliseconds.
- A check that the puzzle is sound: duplicates are pointed out, and a grid with more than one answer is flagged rather than quietly guessed at.
- A way to unstick yourself without abandoning the puzzle — fill in one cell you were missing and go back to solving.
- Techniques you can learn: every page in our library explains, by hand, one of the deductions this solver makes by brute force.
Don’t spoil your own fun
Solving the grid for you is the least interesting thing this page can do. If you are stuck, look up the technique that applies before you paste the whole puzzle in — the point is to finish the next one without coming back here.
How this solver works
It fills the grid by constraint propagation and backtracking: repeatedly place the digit forced in the most constrained cell, and reverse the last choice whenever a cell runs out of candidates. That is the same reasoning our technique pages describe, run exhaustively rather than by eye — which is why it finds an answer to grids that defeat scanning.
One answer, or several
A proper Sudoku has exactly one solution. This solver checks for a second one and says so when it finds it, because a grid with two answers is almost always a puzzle typed in with a digit missing rather than an interesting puzzle.