Sudoku solver
Enter the known digits of your sudoku grid and let the backtracking algorithm find the complete solution in moments. The calculation is done entirely in your browser.
How it works
A valid sudoku has only one solution that follows three rules: each digit from 1 to 9 must appear exactly once per row, once per column, and once in each of the nine 3×3 blocks. Fill in the cells you already know, leave the others empty, and click "Solve".
Which algorithm is used to solve the grid?
The tool uses a "backtracking" algorithm: it tries to place a valid digit in the first empty cell, moves on to the next one, and goes back to try another digit as soon as it reaches a dead end. This method systematically explores all possibilities and is guaranteed to find a solution if one exists, however hard the grid is.
What happens if my starting grid contains a mistake?
The tool first checks that the digits already entered don't break any of the three rules (row, column, block) before starting the solve. If a conflict is detected, or if no solution exists for the grid provided, a clear error message is shown instead of an incorrect result.
Your grid is never sent to a server: the solution is calculated entirely in your browser.