How to Play Sudoku
Sudoku is a logic-based number puzzle on a 9×9 grid. Fill every row, column and 3×3 box with the digits 1–9, each exactly once. No math required — only pure logical deduction.
1. Study the Clues
Pre-filled numbers are your starting clues. Each digit 1–9 may appear only once per row, column and 3×3 box.
2. Find Safe Cells
Scan rows, columns and boxes for cells where only one digit legally fits. Start with these guaranteed moves to unlock the rest of the puzzle.
3. Place & Check
Click a cell, then tap a number. Conflict highlighting shows mistakes instantly. Use Undo to backtrack safely without restarting.
4. Use Notes & Hints
Toggle Notes to pencil candidate numbers into cells. If you're truly stuck, tap Hint — you get 3 per game — to reveal a correct answer.
The 3 Golden Rules of Sudoku
Every Row must contain each digit 1–9 exactly once
Every Column must contain each digit 1–9 exactly once
Every 3×3 Box must contain each digit 1–9 exactly once
Sudoku Difficulty Levels Explained
All four difficulty levels use the same 9×9 grid. The difference is how many clue numbers are given at the start and which solving techniques you'll need.
| Level | Clues Given | Techniques Needed | Avg. Time | Best For |
|---|---|---|---|---|
| 🌱 Easy | 45 clues | Single candidates only | 5–10 min | Beginners & kids |
| 🧩 Medium | 36 clues | Naked pairs, hidden singles | 10–20 min | Casual players |
| 🔥 Hard | 29 clues | X-wing, pointing pairs | 20–40 min | Experienced solvers |
| 💎 Expert | 25 clues | Swordfish, chains | 40–90 min | Puzzle enthusiasts |
Easy Sudoku
Every cell has a single possible answer at any point. Great for learning the rules or a relaxed daily session. No guessing ever required.
Play Easy →Medium Sudoku
Requires scanning pairs of cells together. Perfect for players who've mastered Easy and want a satisfying 15-minute challenge.
Play Medium →Hard Sudoku
Demands advanced elimination chains and careful note-taking. The Notes feature becomes essential at this level.
Play Hard →Expert Sudoku
Only the most dedicated solvers finish these. Multi-step deduction and rare patterns required. Can you beat it without a hint?
Play Expert →Sudoku Tips & Strategies
These proven techniques will help you solve puzzles faster and with fewer mistakes at any difficulty level.
Scan Rows & Columns First
For every digit 1–9, scan which rows and columns already contain it. Where two filled lines cross inside a box, they eliminate possibilities and often reveal the only valid cell for that digit.
Use Pencil Notes
Enable Notes mode and write every possible candidate in each empty cell. As you fill other cells the candidates auto-remove, steadily revealing single options.
Naked Singles
A naked single is any cell where only one candidate remains after eliminating all others in its row, column and box. Always resolve these first — they often unlock a cascade of other cells.
Hidden Singles
A hidden single is when a digit can only go in one cell within a row, column or box — even if that cell appears to have multiple candidates. Scan each unit for digits with just one valid position.
Box-Line Reduction
If all candidates for a digit in a box lie on a single row or column, eliminate that digit from the rest of that row or column outside the box. Essential for hard and expert puzzles.
Never Guess — Always Deduce
Every puzzle on this site has exactly one solution reachable by pure logic. If you feel forced to guess, look harder. Use Undo to safely explore possibilities without penalty.
Why Play on Number Sudoku?
We built the cleanest, fastest free Sudoku experience on the web — no clutter, no mandatory sign-up, just great puzzles.
No Sign-Up Required
Play instantly. No account, email or payment. Your progress saves automatically in your browser.
Works on All Devices
Fully responsive for desktop, tablet and mobile. Large tap targets make it comfortable anywhere.
Daily Challenge
A new hard puzzle refreshes every midnight — the same puzzle worldwide. Build your daily streak.
Smart Hints
3 hints per game reveal a correct cell. Conflict highlighting shows affected cells in real time.
Unlimited Undo
Made a mistake? Undo as many moves as you like. Explore strategies risk-free without restarting.
Dark Mode
Toggle dark mode for comfortable late-night solving. Your theme preference is remembered automatically.
Frequently Asked Questions
Yes — 100% free, forever. No premium tier, no paid hints, no mandatory account. Just open the page and play.
Absolutely. Number Sudoku is fully responsive and works on any smartphone or tablet browser — iOS Safari, Android Chrome and more. No app download needed.
Research suggests regular puzzle-solving can help maintain cognitive sharpness, improve concentration and enhance logical thinking. Sudoku is particularly good for pattern recognition and working memory.
Every day at midnight a new hard-difficulty puzzle is generated using that day's date as a seed, giving every player worldwide the same puzzle. Solve it daily to extend your streak.
Click the Notes (pencil) button in the toolbar — it shows "ON". Numbers you enter now appear as small candidate notes rather than final answers. Toggle Notes OFF to place definitive numbers. Press N on a keyboard as a shortcut.
Yes. All puzzles are generated by a backtracking algorithm that guarantees exactly one valid solution reachable without guessing.
Keyboard Shortcuts
Playing on a desktop? These shortcuts make solving significantly faster.