Find answers to common questions about Sudoku puzzles, our online solver, solving techniques, and more.
Sudoku is a logic-based number-placement puzzle played on a 9Ã9 grid. The goal is to fill the grid so that each row, column, and 3Ã3 box contains all digits from 1 to 9 without repetition.
While Sudoku became popular in Japan in the 1980s, its roots trace back to 18th-century Swiss mathematician Leonhard Euler's work on Latin Squares. The modern version was created by American architect Howard Garns in 1979 and called "Number Place." It was introduced to Japan in 1984 by puzzle company Nikoli, who named it "Sudoku" (meaning "single number").
No! Sudoku requires logical thinking, not mathematical ability. The numbers 1-9 are simply symbols - you could use letters, colors, or any nine different symbols. The puzzle is about pattern recognition and logical deduction, not arithmetic.
Every properly constructed Sudoku puzzle has exactly one solution that can be found through logical deduction alone. However, poorly designed puzzles might have no solution or multiple solutions. All puzzles generated by our tool are guaranteed to have exactly one unique solution.
Mathematically, the minimum number of clues for a Sudoku with a unique solution is 17. However, these puzzles are extremely rare and difficult. Most Sudoku puzzles contain 22-35 clues depending on difficulty level.
Click on any cell in the grid and type a number (1-9) to enter it. Use the "Solve" button for instant solutions using our backtracking algorithm, or use "Human Solve" to see step-by-step solutions using human solving techniques.
Solve: Uses a backtracking algorithm to instantly find the solution. This is the fastest method but doesn't show the logical steps.
Human Solve: Applies human solving techniques (Naked Singles, Hidden Singles, X-Wing, Y-Wing, etc.) step by step. This shows you how a human expert would solve the puzzle and is great for learning.
Pencil Mode allows you to add candidate numbers (possible values) to cells, just like making pencil marks when solving on paper. This helps track which numbers could go in each cell. Toggle it on/off with the "Pencil Mode" button.
When enabled, this feature automatically calculates and displays the possible candidate numbers for each empty cell based on the current puzzle state. It updates in real-time as you place numbers.
Yes! Click the "Share Puzzle" button to copy a link to your current puzzle. The puzzle state is encoded in the URL, so anyone with the link can load and solve the same puzzle.
Yes, our Sudoku Solver is completely free with no subscriptions, registration, or hidden fees. We believe quality puzzle tools should be accessible to everyone.
Once the page is loaded, the solver works entirely in your browser and doesn't require an internet connection. However, you need to be online to initially load the page.
Our algorithm first creates a complete, valid Sudoku solution, then systematically removes numbers while ensuring the puzzle maintains a unique solution. The difficulty is calibrated by the number of clues remaining and the techniques required to solve it.
Yes! Each puzzle is generated algorithmically with randomization, ensuring you get a unique puzzle every time. The generator creates billions of possible puzzles.
The Custom option lets you specify exactly how many clues you want in your puzzle (17-81). Fewer clues generally mean harder puzzles, though the actual difficulty also depends on the pattern of the clues.
The two fundamental techniques are:
These two techniques alone can solve most easy puzzles. For more techniques, see our Strategies page.
No! Every well-constructed Sudoku puzzle can be solved through logical deduction alone. If you find yourself guessing, you're likely missing a logical technique that applies to the current situation. Use our "Human Solve" feature to see which technique you might have missed.
X-Wing is an advanced technique where a candidate appears in exactly two positions in two different rows, and these positions align in the same two columns (forming an X pattern). This allows you to eliminate that candidate from other cells in those columns. It's typically needed for hard and expert puzzles. See our detailed strategies guide for more information.
Our solver works on all modern browsers including Chrome, Firefox, Safari, Edge, and Opera. We recommend using the latest version of your browser for the best experience.
Yes! Our solver is fully responsive and works great on smartphones and tablets. The interface automatically adapts to your screen size.
No. We do not track, store, or collect your puzzles or solving sessions. Everything happens in your browser. See our Privacy Policy for details.
Our tool is intended for learning and personal enjoyment. Please check the rules of any competition or academic assignment before using solver tools, as many prohibit their use.
This means the puzzle as entered has no valid solution. Double-check that you've entered the clues correctly. If you're creating your own puzzle, ensure it follows Sudoku rules and has a valid solution.
Click the "Clear" button to erase all entries and start fresh. This removes both given numbers and your entries.
Currently, progress is saved in your browser's memory for the current session. Use the "Share Puzzle" button to generate a link you can bookmark or save for later.
If your question isn't answered here, please visit our Contact page to get in touch. We're happy to help!
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