Instant, guaranteed answers
A constraint-based search always tries the most restricted cell first, so even expert puzzles are solved in a few milliseconds.
Free online tool · No sign-up
Sudoku Solver with Hints & Step-by-Step Logic
Stuck on a puzzle? Type in the numbers you have and this free sudoku solver fills in the rest in milliseconds. Prefer to crack it yourself? Ask for one hint at a time and see the exact reason behind every move.
- Solves any valid 9×9 puzzle
- Explains each step
- Runs privately in your browser
Enter your sudoku puzzle
Try an example:
Your cluesSolvedHintClash
Number pad
Select a cell and type a digit, or load an example puzzle above.
- Clues
- 0
- Solutions
- –
- Difficulty
- –
- Solve time
- –
Paste or share a puzzle
Solution steps0
Features
Why this sudoku solver is different
Most solvers only dump the answer. This one also teaches, checks and rates your puzzle, so it helps whether you are stuck, curious or verifying your own grid.
Hints that explain why
Each hint places one digit and tells you the logic, for example a naked single in a cell or a hidden single in a box.
Live error checking
Clashing digits turn red the moment you type them, so a typo never sends the solver down the wrong path.
Step-by-step solution log
After solving, open a numbered list of every placement and the reason for it, in the order a person could find them.
Uniqueness and difficulty
See whether your puzzle has exactly one solution and how hard it is, from Easy to Expert, based on the logic it actually needs.
Paste, share and autosave
Paste an 81-character puzzle, share it as a link, and pick up where you left off because your grid saves on this device.
How to use
How to use the sudoku solver
Five quick steps take you from a stubborn grid to a finished, fully checked puzzle.
Enter the clues
Tap or click a cell, then type a digit or use the number pad. Arrow keys move around the grid.
Watch for red
Digits that clash in a row, column or box turn red at once, so you can fix typos before solving.
Choose your help
Press Hint for one explained move, or press Solve to fill the whole grid with an animated reveal.
Review the steps
Open Solution steps to see each placement in order, with the technique that found it.
Check or share
Use Check to verify your own answer, then copy a link so a friend can try the same puzzle.
Techniques
How to solve sudoku: the logic behind every hint
Sudoku has one rule: each row, column and 3×3 box must contain the digits 1 to 9 exactly once. These techniques turn that rule into progress, from the easiest to the most advanced.
Naked single
A cell where eight of the nine digits already appear in its row, column or box. Only one candidate is left, so that digit must go there.
BeginnerHidden single
Pick a digit and look at one row, column or box. If only one cell can hold it, place it there, even when that cell has other candidates.
BeginnerPointing pairs
If a digit's candidates inside a box all line up in one row or column, you can remove that digit from the rest of that line outside the box.
IntermediateNaked pairs and triples
Two cells in a unit that share the same two candidates lock those digits. As a result, you can clear them from every other cell in that unit.
IntermediateX-Wing and Swordfish
When a digit fits in only two cells in each of two rows, and those cells share two columns, the digit can be removed from those columns elsewhere.
AdvancedBacktracking search
How a computer guarantees an answer: try a candidate in the most constrained cell, continue, and step back the moment a contradiction appears.
Computer methodDifficulty
Sudoku difficulty levels explained
Clue count is only a rough guide. What really sets the level is the logic a puzzle demands, which is exactly how our difficulty badge works.
| Level | Typical clues | What it takes |
|---|---|---|
| Easy | 32 to 40 | Naked singles only. Every step is a cell with one candidate. |
| Medium | 27 to 34 | Hidden singles as well as naked singles. |
| Hard | 24 to 30 | Singles run out, so you need pairs, pointing pairs or some trial. |
| Expert | 17 to 26 | Chains, X-Wings or a deep search with many dead ends. |
Our rating first tries to finish the puzzle with singles only. If that works, it is Easy or Medium. If not, the solver measures how much searching the rest needs and labels it Hard or Expert.
Benefits
Benefits of using a sudoku helper
Get unstuck without spoilers
One hint is often all you need, so the rest of the puzzle stays yours to finish.
Learn real techniques
Every hint names the method behind it, so you start spotting the same patterns on your own.
Check your finished grid
Confirm a newspaper or app puzzle in one click instead of waiting for tomorrow's answers.
Verify puzzles you create
Puzzle makers can confirm a grid has exactly one solution before they print or share it.
Private by design
Everything runs in your browser. There is no upload, no account and no waiting on a server.
Fast on any device
Use full keyboard control on a laptop, or the large number pad on a phone or tablet.
FAQ
Sudoku solver FAQ
Can this sudoku solver solve any puzzle?
Yes. It solves any valid 9×9 sudoku, including expert puzzles and the famous “world's hardest” grids, usually in a few milliseconds. If the clues contradict each other, it tells you there is no solution instead of guessing.
How do I get a hint without spoiling the whole puzzle?
Press Hint. The solver places exactly one digit, highlights the row, column or box involved, and explains the logic. Press it again whenever you are stuck, and solve everything else yourself.
Why does it say my puzzle has more than one solution?
A proper sudoku has exactly one answer. When a clue is missing or typed into the wrong cell, several grids can fit, so compare your entries with the original. Also note that a puzzle with fewer than 17 clues can never have a unique solution.
What is the minimum number of clues a sudoku needs?
The answer is 17. In 2012 an exhaustive computer search showed that no 16-clue sudoku has a unique solution, so 17 is the smallest number of clues a valid puzzle can have. You can read more on the mathematics of sudoku.
How do I enter a puzzle quickly?
Type digits straight into the grid and move with the arrow keys. Alternatively, open Paste or share a puzzle and paste an 81-character string with a dot or 0 for each blank. Spaces and line breaks are ignored.
Is using a sudoku solver cheating?
Only if you are competing. For practice, it works like an answer key with a teacher attached: check your work, get unstuck with one hint, and learn the technique so you need fewer hints next time.
Does the sudoku solver work on mobile and offline?
Yes. The grid and number pad are built for touch screens, and all the work happens in your browser. Once the page has loaded, it keeps working without a connection, and your puzzle never leaves your device.
What do the colours in the grid mean?
Dark digits are the clues you entered. Teal digits were filled in by the solver, orange digits came from hints, and red cells show a clash in a row, column or box.
Solve smarter, not just faster
Use the sudoku solver to finish a stubborn puzzle, check your answer or learn one new technique today. Then, when you want another challenge, explore our free online tools.
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