Sudoku Solver

Enter the numbers you know, then hit Solve. Works on any valid Sudoku puzzle.

How to use

  1. Click any cell and type a number (1–9).
  2. Fill in as many clues as you have.
  3. Press Solve — the solution appears in blue.
  4. Hit Clear to start a new puzzle.

Killer Sudoku rules

  • Each row, column, and 3×3 box must contain 1–9 with no repeats.
  • The solver uses backtracking with constraint propagation — it finds the unique solution or reports if the puzzle is invalid.

Try a sample puzzle

What is a Sudoku Solver?

A Sudoku solver is a tool that automatically finds the solution to any valid Sudoku puzzle using logic and backtracking algorithms. You provide the known numbers (the "givens") and the solver fills in every remaining cell while respecting the three core constraints: no repeated digit in any row, column, or 3×3 box.

How does the solver work?

This solver uses a backtracking algorithm with minimum-remaining-values (MRV) heuristics. Instead of filling cells left-to-right, it always picks the empty cell with the fewest legal candidates first — dramatically reducing the search space compared to a naive approach. Most puzzles, even hard ones, solve in under a millisecond.

Is every Sudoku puzzle solvable?

Only if the given clues are consistent and don't violate the rules. A properly constructed puzzle also has exactly one solution. If you enter conflicting clues (e.g. two 5s in the same row), the solver will detect this and report the puzzle as invalid rather than returning a wrong answer.