# Sudoku puzzle rules

Rules of **sudoku puzzle** are very simple, and that makes its so popular.

Sudoku is a 9 by 9 square. These cells are grouped into 9 smaller squares, 3 by 3 cells each.
It is necessary to place the numbers from 1 to 9 in all cells in such a way that in each row, in each column and in each small square, the numbers appear exactly once.

Some of the cells are already filled in to make the task easier. The more empty cells, the more difficult the puzzle.

## Print sudoku

To print Sudoku on any page of our site, click the `Print` button or hotkeys `Ctrl+P`.

## How to use online sudoku on this site

Click on an empty square so that it changes color. Then click on the desired number in the right column.

To erase a digit, click on an empty cell in the right column. The numbers you enter are displayed in blue, the rest in black.
If you make a mistake, all incorrect cells will be highlighted in red.

Your solution is automatically saved to your browser's local storage.

When the puzzle is solved, Sudoku will be marked with

### Example of online sudoku

Solve sudoku