Sudoku
Classic 9×9 Sudoku with four difficulty levels — Easy, Medium, Hard, and Expert. Features a live timer, mistake counter, pencil notes, and 3 hints per puzzle. Beat your best time!
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How To Use
Select a difficulty and click 'New Game'. Click a cell to select it, then click a number (or press 1–9 on your keyboard) to fill it in. Wrong entries are highlighted in red. Use Notes mode (📝) to pencil in candidate digits. Use a Hint (💡) to reveal a cell when you're stuck. Finish all 81 cells correctly to solve the puzzle!
Key Features
Classic 9×9 Sudoku grid with proper 3×3 box constraints
Four difficulty levels: Easy (~51 clues), Medium (~41), Hard (~35), Expert (~29)
Live timer to track your solving speed
Mistake counter that highlights wrong entries in red
Pencil notes mode to mark candidate digits in cells
3 hints per puzzle — reveal a random cell's correct value
Auto-clear notes when a number is placed in a row, column, or box
Keyboard support: numbers 1–9, Backspace to erase, N for notes, arrow keys to navigate
Best time leaderboard per difficulty saved in your browser
Procedurally generated puzzles using backtracking with MRV uniqueness guarantee
What Is This?
Sudoku is a classic logic-based number placement puzzle. The goal is to fill a 9×9 grid so that every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once. No math required — just pure deductive reasoning!
Why Use This?
Sudoku is one of the world's most popular brain-training games. Regularly solving Sudoku puzzles improves logical thinking, concentration, and short-term memory. Our generator creates fresh puzzles every time, so you'll never run out of challenges.
Frequently Asked Questions
How is the puzzle difficulty determined?
Difficulty is controlled by how many starting clues are given. Easy puzzles have ~51 clues (fewest empty cells), while Expert puzzles have only ~29 clues, requiring advanced logical deduction.
Are the puzzles guaranteed to have a unique solution?
Yes — Easy, Medium, and Hard puzzles are generated with a uniqueness check. Expert puzzles also use uniqueness checking for the first 45 removals, making them virtually always unique.
What does Notes mode do?
Notes mode lets you place small 'pencil marks' inside a cell to keep track of possible digits. Notes are automatically cleared from a cell's row, column, and box when you place the correct number.
How do hints work?
You get 3 hints per puzzle. Each hint reveals the correct value for a random empty or incorrectly filled cell. Use them wisely on Expert puzzles!