Sudoku Solver: Solve Any Puzzle Instantly
Type in the numbers from any Sudoku puzzle, book or app, and get the complete solution in an instant. Free, no sign-up, and it flags mistakes as you type.
How the Sudoku solver works
This solver uses backtracking, the same reliable method computers have used to solve Sudoku for decades. It places a valid digit in the first empty cell, moves to the next, and keeps going. Whenever no digit fits a cell, it backtracks to the last guess and tries the next possibility instead. Repeated thousands of times per second, this always finds the solution if one exists — and it runs entirely in your browser, so your puzzle never leaves your device.
Unlike a human solver, backtracking doesn't need naked singles, hidden pairs or X-Wings to make progress. That means it solves easy and expert puzzles in the same fraction of a second. If you want to learn the logical techniques a person uses instead, see our complete guide on how to play Sudoku.
How to use this Sudoku solver
- Enter your puzzle. Click any cell in the grid and type the number printed there, or use the number pad. Repeat for every filled-in cell in your puzzle.
- Watch for conflicts. If a number repeats in its row, column or 3×3 box, the offending cells turn red immediately so you can fix a typo before solving.
- Press Solve Puzzle. The solver fills in every remaining cell with the correct digit.
- Start a new puzzle. Press Clear to wipe the grid, or Load Example to see the solver work on a sample puzzle first.
Tip: Double-check your entries against the original puzzle before solving. Since a real Sudoku always has a solution, a "no solution" result almost always means one digit was typed in the wrong cell.
Sudoku solver FAQ
How does this Sudoku solver work?
It uses backtracking: the solver tries a valid digit in the first empty cell, moves on, and backtracks to try another digit whenever it reaches a dead end. It repeats this until every cell is filled correctly, which takes a fraction of a second even for hard puzzles.
Can it solve any Sudoku puzzle?
Yes, as long as the puzzle you enter is valid. It solves easy, medium, hard and expert grids equally fast, since backtracking doesn't get slower for harder puzzles the way a human solver does.
Why does it say a puzzle has no solution?
This means at least one of the numbers you entered was typed incorrectly, since a correctly copied Sudoku always has a solution. Recheck the highlighted puzzle against your original grid.
What is the minimum number of clues a Sudoku needs?
17. It has been proven by exhaustive computer search that no Sudoku with 16 or fewer givens has a unique solution, so the solver requires at least 17 numbers before solving.
Is this Sudoku solver free?
Yes. It runs entirely in your browser, with no sign-up, no download and no limit on how many puzzles you solve.
Want to solve the next one yourself? Learn the techniques in our how to play Sudoku guide, or play a free Sudoku puzzle right now.
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