Sudoku Solver: Free, Step by Step
Stuck on a puzzle from a newspaper or a book? Type in the numbers and this free Sudoku solver shows you the full solution right away, or walks you through it step by step, naming the technique behind every move.
How to use the Sudoku solver
- Tap a square and enter the numbers from your puzzle. If two numbers conflict, they turn red. Use Erase cell to fix a single square.
- Press Solve to see the complete solution at once.
- Or press Step by step: with each tap you see which square gets solved and which technique does it. Use Back to return to the previous move.
Your numbers stay in one color and the calculated ones in another, so you can always tell what you entered. If you’d like to see the reasoning, turn on Show candidates (automatic notes). In a hurry to test it? Press Try a sample puzzle. To start over, press Clear all.
Step by step: understand it instead of copying it
A full solution takes away the fun, and sometimes you only need one number to get unstuck. That’s why the solver explains every move with the name of the technique. It starts with the naked single (only one number fits in this square) and the hidden single (a number has only one possible place in a row, column or box).
For harder puzzles it moves on to the pointing pair, box/line reduction, the naked pair and hidden pair, and the naked triple and hidden triple. The toughest puzzles call for the X-Wing, XY-Wing, XYZ-Wing and Swordfish. Next time, you’ll be able to spot them yourself.
Sudoku techniques at a glance
- Naked single and hidden single: the basics. Every puzzle starts here.
- Pointing pair and box/line reduction: a number confined to one line inside a box (or to one box inside a line) lets you remove it from the rest of that line or box.
- Naked and hidden pairs and triples: a small group of squares that must hold the same small group of numbers, so those numbers can’t go anywhere else nearby.
- X-Wing and Swordfish: patterns across two or three rows and columns.
- XY-Wing and XYZ-Wing: chains of reasoning across three linked squares.
Want to practice them? The free Sudoku game has five levels, and each one introduces new techniques.
What happens with unusual puzzles
- A puzzle with no solution: we tell you. Most of the time, a number was entered wrongly. Check the red squares against the original.
- A puzzle with more than one solution: we say so and show you one. A well-made Sudoku has just one solution, so make sure you copied every number.
- Very few numbers entered: with fewer than 17 numbers, a puzzle always has many solutions. We show you one and tell you.
- An Evil puzzle: if logical techniques aren’t enough, the step-by-step mode stops and tells you that trial and error would be needed. Then it shows the full solution.
Your puzzle stays private
Everything is calculated in your browser. The puzzle you enter is not sent to us or to anyone else, and it never leaves your device.
Frequently asked questions
Is the Sudoku solver free?
Yes. It’s free, and you don’t need to sign up.
Is my puzzle saved or sent to anyone?
No. All the calculation happens in your browser. The puzzle you enter never leaves your device.
Can I see how the solution is reached?
Yes. Press Step by step. For every move you see the square, the number and the technique used.
Does it work with hard and Evil puzzles?
Yes. The solver finds the solution to any valid puzzle. In step-by-step mode it uses logical techniques and, if they aren’t enough, it warns you when trial and error would be needed.
Why does it say my puzzle has no solution?
Almost always a number was copied wrong. Check the squares marked in red and compare the grid with your original.
Can it solve 16×16, killer or samurai Sudoku?
Not for now. The solver handles classic 9×9 puzzles, the kind in newspapers and magazines.
Can I use it on my phone?
Yes. The grid and keypad are designed for phone screens as well.
Want to play instead?
Try free Sudoku online: five levels, hints that name the technique, and a new Daily Sudoku for every level. For more brain teasers, browse the logic riddles and the riddles section, play the multiplication games, or take the Quiz of the Day from our online quiz games.