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Sudoku Rules
Sudoku is a world-famous number logic puzzle. Fill the 9×9 grid with digits 1–9 so that every row, every column and every 3×3 box contains each digit exactly once. The pre-filled digits are your clues — use pure logic to work out every empty cell. All puzzles on this site are generated on the fly and guaranteed to have exactly one solution.
Tips for Beginners
- Elimination: a digit already present in a row, column or box cannot be repeated inside that unit.
- Last remaining number: if a cell's row, column and box already contain 8 different digits, the cell must hold the missing one.
- Start with the fullest units: rows, columns or boxes with the most clues are usually the easiest to crack.
- Use Check: stuck? Hit the Check button to quickly spot any mistakes in red.
A Short History of Sudoku
The puzzle we call Sudoku was born in 1979, when American architect Howard Garns published "Number Place" in Dell Pencil Puzzles and Word Games. It travelled to Japan in 1984, where the publisher Nikoli renamed it "Sūji wa dokushin ni kagiru" — "the digits must remain single" — later shortened to Sudoku. The modern global boom started in late 2004 when The Times of London began printing daily grids, and within two years the puzzle was running in newspapers on every continent.
Part of Sudoku's endurance is that it asks nothing of you but logic: no vocabulary, no trivia, no math beyond counting to nine. Each of our grids is generated with exactly one solution and can be finished purely by deduction — the three difficulty levels simply change how long you have to dig for that deduction.
자주 묻는 질문
What are the rules of Sudoku?
Fill the 9×9 grid with digits 1–9 so that every row, every column and every 3×3 box contains each digit exactly once. Deduce all empty cells from the given clues.
Does every puzzle have a unique solution?
Yes. All puzzles are generated on the fly and verified to have exactly one valid solution.
What is the difference between the three difficulties?
Harder levels start with fewer clues: Easy has about 43 givens, Medium about 35, and Hard about 29.
Is Sudoku good for your brain?
Sudoku trains logical reasoning, concentration and working memory — a popular mental workout for all ages.
Should I ever guess in Sudoku?
You shouldn't need to. Every puzzle on Cozy Play is solvable by pure logic, and guessing tends to bury an early mistake under twenty wrong digits. If you feel the urge to guess, it usually means a candidate hasn't been eliminated yet — switch to scanning boxes, rows and columns for digits that fit in only one cell.
What is the fastest way to start a Sudoku grid?
Begin with the digit that already appears most often on the board and check every 3×3 box where it's missing. Then repeat with the next most frequent digit. Most easy and medium grids crack open with this one scanning habit before you need any advanced techniques.