Sudoku Online

1. Place digits so none repeats in a row, a column or a box.
2. Begin where the most neighbors are already filled in — those cells have the fewest options.
3. Use notes mode to jot down candidates and cross them off as you go.
4. Try other modes like Killer, X-Sudoku and Windoku for extra rules.

Sudoku Online offers the familiar number puzzle in six different modes: Classic, Master, Killer, X-Sudoku, Points and Windoku. In each one, the aim is to fill the grid so that no digit repeats within any row, column or box, starting from the cells already given as clues. The variant modes add extra rules on top — such as sums in Killer or extra regions in Windoku — for players who want something new. A notes mode lets you pencil in several candidates and cross them off as the grid fills. Beginning where most of the neighboring cells are already filled narrows the options fastest.