Free Online Sudoku Solver
Paste an 81-cell Sudoku, fix live conflicts, solve instantly, reveal one cell at a time, or copy the solved grid — free, private, and fully in your browser.
Key facts
- Free, no sign-up; solves in your browser.
- Type the clues into the 9×9 grid, or paste an 81-character puzzle (0 or . for blanks).
- Highlights conflicting numbers before you solve.
- Tells you when a puzzle has no solution.
- Copy the solved grid as an 81-digit string.
How to Use the Free Online Sudoku Solver
- Enter or paste the puzzle — type clues (1–9) into the 9×9 grid, or open Paste Puzzle and paste an 81-character string. Use 0 or . for blank cells; spaces and line breaks are fine.
- Watch live conflict checks — duplicate digits in a row, column, or 3×3 box highlight in red as you type so you can fix mistakes before solving.
- Click "Solve Sudoku" — the solver fills the complete grid in your browser. Original clues stay darker; solution cells appear in blue.
- Reveal one cell at a time — use Reveal Next Cell to fill a single empty square from the computed solution when you want a hint without dumping the full answer. It does not explain human solving techniques.
- Copy the solved grid — Copy Solved Grid puts an 81-digit solution string on your clipboard for notes, sharing, or another tool.
- Try the example or clear — Load Example fills a classic puzzle (and a matching paste string). Clear Board resets everything for the next Sudoku.
About the Free Online Sudoku Solver
ToolGenie.org's Sudoku solver is a free online Sudoku puzzle solver built for people who need a quick answer, a sanity check, or a single hint. Paste an 81-cell string from another app, type a newspaper grid by hand, highlight conflicts as you go, then solve the full board or reveal the next cell — all without an account.
Everything runs client-side in your browser. Your puzzle is never uploaded to a server, so this Sudoku solver online stays private on desktop, tablet, and phone. There is no signup, no download, and no usage cap.
Under the hood, a backtracking algorithm treats the grid as a constraint-satisfaction problem: it tries digits 1–9 in empty cells and backtracks when a placement breaks a row, column, or 3×3 box rule. That approach solves valid easy through expert 9×9 Sudoku puzzles in milliseconds. If clues conflict or no solution exists, you get a clear message instead of a wrong grid.
Sudoku rules are simple: fill the 9×9 board so every row, column, and box contains 1–9 exactly once. Use this page as a Sudoku checker for mistakes, a full solver when you are stuck, or a guided reveal when you only want the next number.
Frequently Asked Questions (FAQ)
1. How do I solve a Sudoku puzzle online with this tool?
Enter the given numbers on the 9×9 grid (or paste an 81-cell string), fix any red conflict highlights, then click Solve Sudoku. The free online Sudoku solver fills every empty cell in your browser using a backtracking algorithm.
2. Can I paste an 81-digit Sudoku puzzle into the solver?
Yes. Open Paste Puzzle and paste a string with exactly 81 cells. Digits 1–9 are clues; use 0 or . for blanks. Whitespace and common separators are ignored. If the paste has invalid characters or the wrong length, your current grid is left unchanged and you see a precise error.
3. What should I use for blank cells in a Sudoku string?
Use either 0 or a period (.) for empty squares. For example, a line like 53..7.... means 5, 3, blank, blank, 7, then four blanks. Both formats are accepted so you can paste exports from most Sudoku apps.
4. Can this Sudoku solver check my puzzle for mistakes?
Yes. As you type, the Sudoku checker highlights every cell that duplicates a digit in its row, column, or 3×3 box. Solve also re-validates the board and reports conflicting numbers or an unsolvable grid.
5. How can I reveal one Sudoku cell without seeing the full answer?
Click Reveal Next Cell. The tool computes a valid solution (if needed) and fills one previously empty cell. It does not claim to walk through human techniques like naked singles — it is a guided outcome from the computed solution so you can keep playing.
6. Can the solver complete hard or expert Sudoku puzzles?
Yes. Any valid 9×9 Sudoku with at least one solution can be solved — easy, medium, hard, or expert. Extreme difficulty only means fewer clues for humans; the algorithm still finishes in a fraction of a second when a solution exists.
7. Is the Sudoku solver free, and does it keep my puzzle private?
It is 100% free with no signup or usage limits. Solving, pasting, revealing, and copying all happen locally in your browser — puzzle digits are not sent to ToolGenie.org servers.
8. How do I copy the solved Sudoku grid?
After the puzzle is solvable, click Copy Solved Grid. You get an 81-character string of digits 1–9 representing the complete solution, ready to paste into notes or another program.
Tips for Solving Sudoku Puzzles Faster
- Verify pasted clues first: After an 81-cell paste, scan the board and clear any red conflict highlights before you solve or reveal.
- Use conflict highlighting as a checker: Fix duplicates in the highlighted row, column, or box — that alone catches most typing errors.
- Reveal sparingly: One cell at a time keeps the puzzle playable; full Solve is best when you only need the answer.
- Scan dense units: Rows, columns, and boxes with the most clues usually yield the next placement fastest.
- Look for naked singles: If a cell has only one legal digit left, place it — no guessing required.
- Avoid random guesses: Classic Sudoku is pure logic. If you feel stuck, reveal one cell or let the solver confirm the grid.
- Copy results when comparing answers: The 81-digit export is handy for checking a paper solution or saving progress notes.