Sudoku
Play classic 9x9 Sudoku with three difficulty levels, notes, hints, and a mistake counter - free, with no account required.
Fill the 9x9 grid so every row, column, and 3x3 box contains the numbers 1 to 9 exactly once. Choose a difficulty, select a square, and enter numbers using the keypad below, your keyboard, or touch.
Game Over
You made three mistakes. Start a new puzzle to try again.
Puzzle Complete!
How to Play Sudoku
Select an empty square, then enter a number from 1 to 9 using the number pad, your keyboard, or by tapping on touch devices. Every row, every column, and every one of the nine 3x3 boxes must contain each number exactly once - no repeats. The puzzle is solved when the entire grid is filled correctly.
Sudoku Rules
- Each row must contain the numbers 1 to 9, with no repeats.
- Each column must contain the numbers 1 to 9, with no repeats.
- Each of the nine 3x3 boxes must contain the numbers 1 to 9, with no repeats.
- The starting numbers already on the board (shown in bold) can never be changed.
- Every puzzle has exactly one correct solution.
Sudoku Tips for Beginners
- Start with rows, columns, or boxes that already have the most numbers filled in - they have fewer possibilities left to work out.
- Use Notes/Pencil mode to jot down every number that could still go in a square, then narrow those candidates down as you fill in more of the board.
- If a number can only go in one square within a row, column, or box, it belongs there even if other squares still look open.
- Take your time - Sudoku has no time pressure built into the rules, even though this version includes an optional timer.
Easy vs Medium vs Hard Sudoku
Easy puzzles start with more numbers already filled in, leaving fewer squares to work out and making the logical steps more straightforward to spot. Medium puzzles fill in fewer starting numbers, requiring more deduction. Hard puzzles start with the fewest given numbers, demanding more careful use of notes and logic to work through.
Why Play Sudoku?
Sudoku is a relaxing, self-contained logic puzzle - there is no vocabulary or general knowledge required, just careful, step-by-step reasoning. It is a popular way to pass the time, unwind, or enjoy a quiet mental challenge, entirely at your own pace.
Frequently Asked Questions
Is DONToolbox Sudoku free?
Yes. It is completely free, with no download, no account, and no limit on how many puzzles you can play.
How do you play Sudoku?
Fill the 9x9 grid so every row, column, and 3x3 box contains the numbers 1 to 9 exactly once, using the starting numbers already on the board as clues.
Does Sudoku require maths?
No. Sudoku uses logic and deduction, not arithmetic - the numbers 1 to 9 are simply symbols, and no calculation is ever required.
What happens if I make a mistake?
An incorrect entry is clearly marked and counted. After three mistakes, the puzzle ends and you can start a new one.
Can I use notes or pencil marks?
Yes. Turn on Notes mode to jot down candidate numbers in any empty square, then turn it off to enter your final answer as usual.
Can I get a hint?
Yes. The Hint button reveals one correct number for an unsolved square. Hints used are tracked and shown when you complete the puzzle.
Does Sudoku work on mobile?
Yes. The board and controls are designed to work comfortably on desktop, tablet, and mobile devices.
Do I need to create an account?
No. You can play immediately with no account, login, or personal information required.
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