Objective: Fill the 9x9 grid so that each column, each row, and each of the nine 3x3 blocks contains the digits from 1 to 9, only one time each (that is, exclusively). Pencil Marks: The usual approach to solve a Sudoku board is via pencil marks. They remind you which values are still possible for the current cell. You can toggle the pencil marks by clicking on them.

Whether you're a Sudoku beginner or master, test yourself with three levels of difficulty. Everyday is a new challenge.