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Classic Sudoku - Free 9x9 Puzzle Game Online

Classic Sudoku is the world's most popular number puzzle. Fill the 9x9 grid so that every row, column, and 3x3 box contains the numbers 1 through 9 exactly once. With three difficulty levels and unlimited puzzles generated instantly in your browser, you can enjoy endless brain training at your own pace. No account required, no downloads needed — just pure puzzle-solving fun.

How to Play Classic Sudoku

The rules are simple: fill every row, column, and 3x3 box with the numbers 1 through 9, without repeating any number. Start with the pre-filled cells as your clues, use logic to deduce the remaining numbers, and experience the satisfaction of completing each puzzle.

Whether you're a Sudoku veteran or trying the classic format for the first time, our three difficulty levels — Easy, Medium, and Hard — ensure a satisfying challenge every time.

Basics

  • 1

    Fill the Grid

    Your goal is to fill every empty cell in the 9x9 grid with numbers from 1 to 9.

    5
    3
    7
    6
    1
    9
    5
    9
    8
    6
    8
    6
    3
    4
    8
    3
    1
    7
    2
    6
    6
    2
    8
    4
    1
    9
    5
    8
    7
    9
  • 2

    Follow the Rules

    Each row, column, and 3x3 box must contain the numbers 1-9 exactly once. No repeats allowed!

    Each Row

    5
    3
    4
    6
    7
    8
    9
    1
    2

    Each Column

    5
    6
    1
    8
    4
    7
    9
    2
    3

    Each 3x3 Box

    5
    3
    4
    6
    7
    2
    1
    9
    8
  • 3

    Use Notes

    Tap the pencil icon to enable notes mode. This lets you mark possible numbers in each cell to help narrow down the correct answer.

    Notes Mode

    1 3 5 7 9
    →

    Solved

    5
  • 4

    Complete the Puzzle

    Fill in all the cells correctly to complete the puzzle. Try to beat your best time!

    5
    3
    4
    6
    7
    8
    9
    1
    2
    6
    7
    2
    1
    9
    5
    3
    4
    8
    1
    9
    8
    3
    4
    2
    5
    6
    7
    8
    5
    9
    7
    6
    1
    4
    2
    3
    4
    2
    6
    8
    5
    3
    7
    9
    1
    7
    1
    3
    9
    2
    4
    8
    5
    6
    9
    6
    1
    5
    3
    7
    2
    8
    4
    2
    8
    7
    4
    1
    9
    6
    3
    5
    3
    4
    5
    2
    8
    6
    1
    7
    9

Tips & Strategies

Scan Rows and Columns

Pick a number (like 1) and scan each row, column, and box to see where it can go. This systematic approach helps you find placements you might otherwise miss.

Look for Naked Singles

When a cell can only contain one possible number, fill it in immediately. These "naked singles" often unlock a chain of other cells.

Use Pencil Marks

For harder puzzles, use notes mode to mark all possible numbers in each cell. Then eliminate options by checking what numbers already exist in the same row, column, and box.

Hidden Singles

If a number can only go in one cell within a row, column, or box, place it there — even if the cell has other candidates. This technique is essential for medium and hard puzzles.

Controls

Mouse / Trackpad

Click on any empty cell to select it, then click a number (1-9) to fill it in. Click the pencil icon to toggle notes mode, and use Clear to remove a number.

Touch Screen

Tap any empty cell to select it, then tap a number to place it. Tap the pencil icon to enable notes mode for marking possible candidates in each cell.

Frequently Asked Questions

What is Classic Sudoku?

Classic Sudoku is a logic-based number puzzle played on a 9x9 grid divided into nine 3x3 boxes. The objective is to fill every row, column, and box with the numbers 1 through 9, without repeating any digit. It's the original and most popular form of Sudoku, enjoyed by millions worldwide.

How is Classic Sudoku different from Mini Sudoku?

Classic Sudoku uses a 9x9 grid with numbers 1-9 and 3x3 boxes, while Mini Sudoku uses a smaller 6x6 grid with numbers 1-6 and 2x3 boxes. Classic puzzles are more challenging and take longer to solve (81 cells vs 36), making Mini Sudoku a great starting point for beginners.

What do the difficulty levels mean?

Difficulty is determined by the number of pre-filled clues given at the start:

🌱

Easy

41 clues given

Great for warming up

🌿

Medium

31 clues given

A solid challenge

🌳

Hard

23 clues given

For experienced solvers

Are the puzzles generated randomly?

Yes! Every puzzle is generated fresh in your browser using a backtracking algorithm. This means you get a unique puzzle every time you play, with an unlimited supply of challenges at every difficulty level.

Is my progress saved?

Yes, your current game progress is automatically saved in your browser's local storage. If you close the page and come back later, you can continue right where you left off. Your best times for each difficulty level are also saved.

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