How to Play
Sudoku is a logic-based number puzzle. The goal is to fill a 9x9 grid so that every row, column, and 3x3 box contains the digits 1 through 9 exactly once.
- Tap a cell to select it, then tap a number to place it
- Notes mode lets you pencil in candidates — toggle it with the pencil button
- Hints reveal the correct number for the selected cell (3 per game)
- Undo takes back your last move
- Error checking highlights mistakes in red automatically
- Use keyboard arrow keys to navigate and number keys to enter digits
Difficulty Levels
Choose from four levels that control how many cells start filled:
- Easy — plenty of givens, great for beginners
- Medium — requires basic elimination techniques
- Hard — needs more advanced logic and notes
- Expert — minimal clues, for experienced solvers
Frequently Asked Questions
How does Sudoku work?
Sudoku is a logic puzzle played on a 9x9 grid. The goal is to fill every row, column, and 3x3 box with the digits 1 through 9 exactly once. No math is required — only logical deduction.
What are the difficulty levels?
There are four difficulty levels: Easy (many given digits), Medium (basic elimination), Hard (advanced logic needed), and Expert (minimal clues for experienced solvers).
Can I use notes while solving?
Yes. Toggle Notes mode with the pencil button to pencil in candidate numbers in a cell. This helps you track possibilities without committing to a final answer.
Is there a time limit?
There is no time limit. A timer tracks how long you take, and your best times per difficulty level are saved automatically.
Are the puzzles randomly generated?
Yes. All puzzles are generated in your browser with guaranteed unique solutions. Each game is different.
About
Sudoku originated in 18th-century Switzerland as "Latin Squares" and was popularized in Japan in the 1980s under the name "Sudoku" meaning "single number." It became a worldwide phenomenon in the 2000s.
Our version features a clean, modern interface with dark and light mode support, stats tracking with best times per difficulty, and a responsive layout that works on any device. All puzzles are generated in your browser with guaranteed unique solutions.
From the build: we rebuilt the generator twice before we shipped. The first version produced Hard and Expert boards that had multiple valid solutions — technically still Sudoku, but it broke the rule that good Sudoku has exactly one answer. The current generator verifies uniqueness before serving a board, which is why the harder difficulties take a moment longer to load. Worth it. We also pushed the cell hit-area larger than it looks on mobile after watching people misfire on touchscreen taps during testing.