Sudokutoon gives this fun puzzle game a modern, colorful facelift. Just like in regular Sudoku, there are nine 9x9 boxes. Some have numbers in them, some are empty. You need to have one of each number from one to nine in each square, in each vertical line, and in each horizontal line. No number can be missing and no number can be repeated. To add a number to a blank square, click on it to scroll through all of the numbers. If a number is already in the 9x9 square you are playing in, that number will turn red if you try to play it in another square.