The game is given a playing field of 9x9 cells. You need to fill in the empty cells with numbers from 1 to 9. You can put the numbers so that in a row, in a column and in a small 3x3 square the number appears only once. You are allowed to make only 2 mistakes. You can make notes in the cells and erase the contents. The current game is saved. The game has several difficulty levels.