How to Solve Sudoku Online — Free Solver (2026)

Use the free Brevio Sudoku Solver to solve any Sudoku puzzle instantly — enter the given clues, click Solve, and the solution appears in seconds using a backtracking algorithm.

How to Use the Sudoku Solver

1. Click Load Sample to start with a pre-loaded puzzle, or click Clear to start from scratch.
2. Type your puzzle's given numbers into the grid. Each cell accepts a digit from 1 to 9.
3. Conflict cells are highlighted in red as you type, so you can spot input errors immediately.
4. Click Solve to run the solver. The completed solution fills the grid in blue.
5. If no solution exists, an error message appears.

How the Solver Works

The solver uses backtracking search: it finds the first empty cell, tries digits 1–9 in order, checks whether each digit is valid given the current row, column, and 3×3 box, and moves on if valid. If it reaches a dead end (no valid digit fits), it backtracks to the previous cell and tries the next digit. This exhaustive search always finds a solution if one exists, and correctly reports "no solution" when the puzzle has no valid completion.

Sudoku Rules

A valid Sudoku solution fills a 9×9 grid so that every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once. The starting puzzle provides some clues (given numbers), and the solver fills in the rest. A well-formed Sudoku has exactly one solution.

Frequently Asked Questions

Can I solve any Sudoku puzzle?

Yes. Enter the clue numbers and click Solve. Standard 9×9 puzzles are supported.

What if my puzzle has no solution?

The solver will display "No solution found" — which usually means a clue was entered incorrectly.

Is the solver free?

Yes, completely free with no sign-up required.

How fast is the solver?

Most puzzles solve in under a millisecond. Even the hardest hand-crafted puzzles complete in well under a second.