Introduction
Sudoku is a classic logic puzzle where you fill a 9x9 grid with digits 1 through 9. Each row, column, and 3x3 box must contain every digit exactly once. The puzzle uses logic rather than guessing, making it a satisfying way to practice focus, deduction, and pattern recognition.
How to Play
Select an empty cell, then enter a digit using the keyboard or on-screen number pad. Check the row, column, and 3x3 box before placing a number. Use notes to track candidates, hints if you get stuck, and error checking to learn from conflicts. Complete the full grid to solve the puzzle.
Features
- •Classic 9x9 Sudoku puzzles
- •Multiple difficulty levels for casual and advanced play
- •Notes and candidate tracking support
- •Hints and error checking for learning
- •Timer and move counter
- •Keyboard and touch-friendly input
- •Free browser puzzle with no installation
Sudoku Is Logic, Not Arithmetic
Sudoku uses numbers, but it is not a math calculation game. The digits are symbols that must fit the row, column, and box rules. You do not add or multiply them. Good solving comes from eliminating impossible choices until only one option remains.
How to Improve at Sudoku
Start by scanning rows, columns, and boxes for missing digits. Look for cells with only one possible value, then update nearby candidates. As puzzles get harder, use notes to avoid holding too much information in your head.
Avoid Guessing Too Early
Guessing can solve some puzzles, but it makes mistakes harder to trace. Before guessing, look for singles, hidden singles, locked candidates, and pairs. These techniques often unlock the next step without trial and error.
Choosing a Difficulty
Easy puzzles are good for speed and confidence. Medium puzzles introduce more candidate tracking. Hard and expert puzzles require stronger pattern recognition and patience.
Sudoku Technique Guide
Common solving techniques from beginner to more advanced play.
| Technique | What It Means | Best For |
|---|---|---|
| Naked single | A cell has only one possible digit | Beginner progress |
| Hidden single | A digit has only one possible place in a unit | Finding overlooked moves |
| Locked candidate | Candidates in a box are limited to one row or column | Clearing nearby candidates |
| Naked pair | Two cells share the same two candidates | Reducing harder sections |
| Scanning | Checking rows, columns, and boxes systematically | Every difficulty |
Difficulty Guide
What to expect from each type of puzzle.
| Difficulty | Typical Experience | Recommended Approach |
|---|---|---|
| Easy | Many obvious singles | Scan and place confidently |
| Medium | More candidate tracking | Use notes and check boxes carefully |
| Hard | Fewer direct placements | Look for hidden singles and locked candidates |
| Expert | Requires advanced patterns | Work slowly and avoid guessing |
Frequently Asked Questions
What are the rules of Sudoku?
Fill the 9x9 grid with digits 1 through 9 so each row, each column, and each 3x3 box contains every digit exactly once.
Do I need math skills to play Sudoku?
No. Sudoku uses digits, but solving is based on logic and pattern recognition, not arithmetic.
What are notes in Sudoku?
Notes are small candidate numbers that help you track which digits might still fit in an empty cell.
Should I guess when stuck?
Try logical techniques first, such as singles, hidden singles, locked candidates, and pairs. Guessing can make mistakes harder to find.
Does every Sudoku puzzle have one solution?
Well-designed Sudoku puzzles are created to have a unique solution.