How to Play Sudoku
Sudoku is the world's most popular number puzzle. Fill a 9×9 grid so every row, column, and 3×3 box contains the digits 1 through 9 exactly once. Pure logic — no math required!
📋 Rules
The Grid
A 9×9 grid divided into nine 3×3 boxes. Some cells are pre-filled with "given" numbers that cannot be changed.
Basic Rule
Every row, every column, and every 3×3 box must contain each digit from 1 to 9 exactly once. No repeats allowed.
Pencil Marks
Use pencil marks (notes) to track which numbers are possible in each empty cell. Toggle note mode to add or remove small candidate numbers.
Conflicts
If you place a number that violates the rules, it will be highlighted in red. Fix conflicts to continue.
Difficulty
Easy puzzles have 49 given numbers, Medium has 37, and Hard has only 29. Fewer givens means more deduction required.
🧠 Strategy Tips
- Start with "naked singles" — cells where only one number is possible based on the row, column, and box.
- Use "hidden singles" — a number that can only go in one cell within a row, column, or box.
- Pencil mark everything in harder puzzles. Visual scanning of candidates reveals patterns.
- Look for "pointing pairs" — when a number in a box is restricted to one row or column, it eliminates that number elsewhere in that row or column.
- Work systematically: scan each number 1-9 across the whole grid before moving on.
❓ Frequently Asked Questions
Does Sudoku require math?
No! Despite using numbers, Sudoku is purely a logic puzzle. You could replace the digits with any 9 unique symbols and it would work the same.
Can a Sudoku puzzle have multiple solutions?
A properly constructed puzzle has exactly one unique solution. All puzzles on this site are guaranteed to have one solution.
What is the minimum number of givens for a unique puzzle?
The proven minimum is 17 given numbers. Any fewer and the puzzle will have multiple solutions.