Sudoku Rules: How to Play and Win on ilsudoku.it
Sudoku is one of the world's most popular puzzle games. Although it involves numbers, it requires no mathematical knowledge — it's entirely based on logic. In this page, you'll find everything you need to know about Sudoku rules and how to complete your first grid.
The Objective of the Game
The goal is to fill a 9×9 grid with the digits 1 through 9 so that each number appears exactly once in every row, every column, and each of the nine 3×3 blocks (also called "subgrids" or "regions").
The Three Fundamental Rules
To solve a classic Sudoku, you must follow three simple but strict constraints:
- Each row must contain the numbers 1 through 9: There can be no duplicates within the same horizontal row.
- Each column must contain the numbers 1 through 9: There can be no duplicates within the same vertical column.
- Each 3×3 block must contain the numbers 1 through 9: The grid is divided into 9 smaller squares (separated by thicker lines). Each square must contain all digits without repetitions.
How to Start Playing
When you start a game on ilsudoku.it, you'll see some cells are already filled. These are your starting clues. More clues usually mean an Easy level; fewer clues mean the challenge will be Hard or Extreme.
Solving Steps
- Scanning: Look across the grid to find numbers that appear frequently. If the number "5" appears in almost every block except one, use logic to find where it must go in the missing block.
- Elimination: Look at an empty cell and check its row, its column, and its block. Which numbers are missing? If only one number between 1 and 9 is not present in any of these three areas, then that number must go in that cell.
- Using Notes: In advanced levels, it's almost impossible to remember all possibilities in your head. Use our Notes feature to mark small numbers (candidates) within the cells.
Common Mistakes to Avoid
- Guessing: Sudoku is a game of pure logic. Every puzzle on ilsudoku.it has only one correct solution reachable without ever having to guess.
- Forgetting Blocks: Players often focus only on rows and columns, forgetting that the 3×3 block is just as important a constraint.
Differences in Killer Sudoku
If you are playing Killer Sudoku, remember there's an extra rule: the sum of numbers within a "cage" must match the number indicated in the corner, and digits cannot repeat within the cage.
Now that you know the Sudoku rules, you're ready for the challenge! Choose a difficulty level from our Home Page and start playing now.