About the Sudoku Solver
Sudoku Solver solves any Sudoku puzzle you give it. Type the numbers you know into the grid, or paste the puzzle as 81 digits (with 0 or a dot for empty squares), and press Solve to see the finished grid in a moment. The solver checks the puzzle first, marking any numbers that break the rules in red, and tells you whether the puzzle has exactly one solution, more than one or none. It is useful for checking your own answer, for getting unstuck and for testing puzzles you write. Everything runs in your browser.
Updated October 2026
How to use the Sudoku Solver
- 1Type the given numbers into the grid, or paste 81 digits and press Load puzzle.
- 2Fix any numbers marked in red.
- 3Press Solve.
- 4Read the solution in the grid, or copy it as text.
- 5Press Edit puzzle to go back and change something.
How the solver works
The solver uses a method called backtracking with constraint checking. It finds the empty square with the fewest possible numbers, tries each one in turn and moves on. If it reaches a dead end, it steps back and tries another number. Because it always picks the most constrained square first, even the hardest puzzles are solved almost instantly.
Using it to learn
Do not just copy the answer. Use the solution to check your work and see where you made a mistake, or reveal one square at a time. Look at why each number must be where it is. If you are practising, play the Sudoku game and use this tool only to confirm.
- Check your finished grid
- Find the first wrong number in a stuck puzzle
- Test puzzles you made yourself
- Confirm that a puzzle has one solution
Typing a puzzle quickly
Click the first square and type a digit; use the Tab key to move. For a printed puzzle, it is faster to type the numbers row by row in the paste box, with a 0 for each blank, and press Load puzzle.
More puzzles
Play the Sudoku game, print mazes with the Maze Generator and word puzzles with the Word Search Generator. The Memory Test and Minesweeper offer other challenges.
Features
- Solves any valid Sudoku in a moment
- Type into the grid or paste 81 digits
- Marks numbers that break the rules
- Tells you if the solution is unique
- Copy the answer as text
- Private: nothing is uploaded
Frequently asked questions
How do I use the solver?
Enter the given numbers, leave the unknown squares empty and press Solve. The solved grid appears with the numbers you gave unchanged.
What if it says there is no solution?
Check that every number you typed is right. A single wrong number can make a puzzle impossible.
What does more than one solution mean?
A proper puzzle has exactly one solution. If the solver says there are several, some given numbers may be missing, and it shows one of them.
How many numbers must I give?
At least 17 are needed for a single solution, and the solver asks for that many.
Can I paste a puzzle from a website?
Yes. Paste 81 digits in a row, using 0 or a dot for empty squares. Line breaks and spaces are ignored.
Is it fair to use a solver?
For learning, it is a good way to check your answer or see the next step. If you want a challenge, try the Sudoku game instead.
How fast is it?
Normal puzzles are solved in a few milliseconds, because the solver always works on the square with the fewest options.
Why are the numbers I typed shown in a different colour?
The numbers you typed are the given clues and appear in bold. The numbers the solver adds are shown in the accent colour, so you can see what was filled in.
Can the solver handle very hard puzzles?
Yes. It works through every possibility in an organised way, so even puzzles made to be difficult for humans are solved quickly.
Is my puzzle uploaded?
No. The puzzle is solved in your browser.