Sudoku Solver

Our free Sudoku Solver fills in any 9×9 sudoku in a fraction of a second, and it can also show you how to solve it yourself, one explained step at a time. Type in your puzzle, press Solve, and you get the answer and a difficulty estimate. It runs in your browser on a desktop, tablet or phone, with nothing to install.

What the sudoku solver does

• Checks your entry: if a digit appears twice in a row, column or box, both cells turn red and the solver tells you where the clash is, so typing mistakes are easy to spot.
• Solves instantly: a backtracking search finds the answer, even for puzzles built to be very hard, usually in a few thousandths of a second.
• Tells you when a puzzle is broken: it counts solutions up to two. If there is no way to fill the grid it says “No solution”, and if there is more than one way it says so and shows one valid answer. A proper sudoku has exactly one solution, and it needs at least 17 clues to have only one.
• Estimates difficulty: Easy puzzles need only singles, Medium puzzles need pointing or box/line reduction, Hard puzzles need pairs or triples, and Expert puzzles need more than the techniques this tool explains.

How to use it

1. Enter the puzzle. Tap a cell, then tap a digit on the number pad, or use the arrow keys and type 1 to 9. Backspace, Delete or 0 clears a cell. You can also paste the puzzle as 81 characters, row by row, using 0 or a dot for each blank.
2. Press Solve. The answer appears in green, with the number of clues, the solver time and the difficulty. Copy answer copies all 81 digits.
3. Learn the solution with Steps. Each press of Next step (or the N key) makes the simplest logical move available from the current grid and explains it. Back undoes a step, and Run to end lists every step.
4. Play from here. Play it starts the puzzle fresh so you can solve it yourself with a timer. Play from here, in the Steps tab, keeps the steps you have already taken. Check marks wrong digits in red, and Hint explains and fills the next move.

The Load a puzzle menu has examples from easy to very hard, the example puzzle from Wikipedia’s sudoku article, and two demo grids with no solution and with two solutions. Puzzles you open in Solve, Steps or Play are added to it.

The techniques in Step-by-step mode

Small gray digits in empty cells are candidates, the digits that could still go there. Red candidates are the ones the current step removes, and the highlighted cells show the row, column or box the step is about. Cells are named by row and column, so r3c5 is row 3, column 5.

• Hidden single: a digit can only go in one cell of a row, column or box.
• Naked single: a cell has only one candidate left.
• Pointing: inside a box, a digit’s candidates all lie on one row or column, so it can be removed from the rest of that line.
• Box/line reduction: in a row or column, a digit’s candidates all sit inside one box, so it can be removed from the rest of that box.
• Naked pair or triple: two cells share the same two candidates, or three cells share three, so those digits can be removed from the rest of the unit.
• Hidden pair: two digits can only go in the same two cells, so those cells lose every other candidate.

Some very hard puzzles need techniques beyond this list. When none of these steps works, the solver makes a guess and labels it clearly: it picks a cell with few candidates and places the digit from the full solution. That is trial and error checked against the answer, not logic, and the difficulty is then shown as Expert.

Tips for solving sudoku yourself

• Scan for hidden singles first. Pick a digit and check each box in turn.
• Write in candidates when you get stuck. Pairs and pointing are far easier to see.

FAQ

Is the Sudoku Solver free?

Yes. It’s free with no account, no download and no limit on puzzles.

Can it solve any sudoku?

It solves any standard 9×9 sudoku that has a solution, and it tells you when a grid has none or has more than one. It doesn’t handle variants such as killer or jigsaw sudoku.

Is my puzzle saved?

Your grid, your Play progress, best times and recent puzzles are saved in your browser on this device only.

More puzzles to play

Want a fresh grid? Play classic Sudoku, or add sums to the rules with Killer Sudoku.