Stuck on a hard puzzle? This free Sudoku solver fills in any 9x9 grid in a split second. Type your numbers, press Solve puzzle and see the full answer, or press Next step to get one logical hint at a time and finish it yourself. No login, no download and no limits.
A fast and free Sudoku puzzle solver
Our Sudoku puzzle solver works with any classic 9x9 Sudoku: puzzles from newspapers, puzzle books, apps or the printable Sudoku sheets on 7cub. It uses a smart search that always tries the most constrained cell first, so even very difficult puzzles with only 17 starting numbers are usually solved in less than a second.
The solver does more than give you the answer. It also checks your puzzle, tells you if a number breaks the rules, and tells you whether the puzzle has one unique solution, several solutions or no solution at all. That makes it a handy tool for players, teachers and anyone who creates their own puzzles.
How to use the Sudoku solver
- Enter your puzzle. Tap a cell and choose a number from the pad, or click a cell and type with your keyboard. Use the arrow keys to move around and Backspace to clear a cell.
- Or paste it. Type or paste all 81 digits in one line into the paste box (use 0 or a dot for empty cells) and press Load.
- Press Solve puzzle to see the complete answer. Your own numbers stay white; the solved numbers appear in orange.
- Press Hide answer to go back to your original puzzle at any time.
- Want to try it first? Press Load example to load a sample puzzle.
Solve it step by step with hints
If you would rather solve the puzzle yourself, the Next step button is your friendly coach. Each press fills in just one cell, highlights it in green and explains why that number belongs there, for example:
- Naked single: only one number is possible in a cell, because every other number already appears in its row, column or box.
- Hidden single: a number can only go in one place within a row, a column or a 3x3 box.
When a puzzle needs more advanced techniques, the solver still gives you the correct next number so you are never stuck. Step-by-step hints are a great way to learn real Sudoku strategies instead of just copying the answer.
Check your puzzle for mistakes
Press Check at any time. The Sudoku problem solver looks at every row, column and box and highlights repeated numbers in red. It also tells you if the numbers you entered can still lead to a valid solution. This is perfect when you have typed a puzzle from a book and want to be sure there are no typing mistakes before you solve it.
Why does a Sudoku need at least 17 numbers?
Mathematicians have proved that a classic Sudoku with a single unique solution needs at least 17 given numbers. With fewer clues, there are always several possible answers. That is why our solver asks for at least 17 numbers before it starts. Most puzzles in newspapers and books have between 22 and 35 clues.
Who uses a Sudoku solver?
- Puzzle fans who want to check their finished grid or get past one tricky spot without giving up.
- Newspaper readers who don't want to wait until tomorrow's paper for the answer.
- Teachers and parents who use Sudoku to teach logic and need a fast answer key.
- Puzzle creators who want to make sure a new puzzle has exactly one solution before sharing it.
- Beginners who want to learn how solving works by following the hints one step at a time.
Whatever your reason, the tool is designed to be calm, clear and easy to use – just like every game on 7cub.
Sudoku solving tips
- Start with the easy cells. Look for rows, columns or boxes that are almost full.
- Scan each number. Pick a number such as 1 and look where it can still go in every box.
- Use pencil marks. On paper, write small candidates in the corners of empty cells.
- Never guess too early. A logical single is almost always hiding somewhere on the grid.
- Use the hint button sparingly. One hint is often enough to unlock the rest of the puzzle.
Features
- 100% free Sudoku solver – no login, no sign-up and no download
- Solves easy to extremely hard puzzles, usually in milliseconds
- Step-by-step hints with clear explanations
- Mistake checker that finds conflicts and unsolvable grids
- Tells you if a puzzle has a unique solution
- Paste a full puzzle as 81 digits
- Your grid is saved on your device automatically
- Works on phones, tablets and computers
Frequently asked questions
Is this Sudoku solver free?
Yes. The Sudoku solver on 7cub is completely free to use, as often as you like, with no account needed.
Can it solve any Sudoku?
It can solve any valid classic 9x9 Sudoku, including the hardest puzzles. If a puzzle has no solution, the solver will tell you.
How do I enter a puzzle quickly?
Paste all 81 numbers in one line into the paste box, reading each row from left to right. Use 0 or a dot for empty cells, then press Load.
Can I get only a hint instead of the full answer?
Yes. Press Next step to reveal one cell at a time with an explanation, so you can keep solving the puzzle on your own.
Does it work on my phone?
Yes. The grid and number pad resize automatically for Android phones, iPhones, tablets and computers.
Is my puzzle private?
Yes. Everything runs in your own browser. Your puzzle is only saved on your device and is never sent anywhere.
Ready to play instead of solve? Try Sudoku online, print a printable Sudoku or explore all our Puzzle Games.