Sudoku puzzles
Fill the grid with 1 to 9 and no repeats.
Classic Sudoku starts with some digits already in place, and an Easy board can be finished with singles alone. Killer Sudoku starts with an empty grid split into cages, each printed with its sum, so the sums take the place of the givens. 6x6 Sudoku and 6x6 Killer Sudoku play the same way on a six by six grid with the digits 1 to 6, which makes a quicker puzzle.
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Sudoku
Fill the grid so every row, column and box holds 1 to 9.
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Killer Sudoku
Fill the grid so every cage adds up to its sum.
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6x6 Sudoku
Fill the small grid so every row, column and box holds 1 to 6.
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6x6 Killer Sudoku
Fill the small grid so every cage adds up to its sum.
About these games
Every puzzle has exactly one solution. The menu beside New puzzle offers Easy, Medium, Hard or Any, and your choice holds for each new puzzle until you change it. The rating comes from the techniques a puzzle needs, not from how many digits it shows: Easy falls to singles, Medium also needs eliminations such as pointing pairs and naked pairs, and Hard needs techniques beyond those.
If you are new to Sudoku, 6x6 Sudoku is the quickest way in: most puzzles rate Easy and there are only 36 cells to fill. Move on to the nine by nine grid once singles come easily. Killer Sudoku suits players who like arithmetic, since you work from cage sums instead of givens, and 6x6 Killer Sudoku is a shorter introduction to it.
Notes, Undo and unlimited hints are there when you need them, though a puzzle finished after a hint, or with Check entries on, is not recorded as a win. All four are free in your browser without signing in, and signing in adds a daily puzzle for each, the same for everyone that day. Sudoku is played alone, so there are no online tables.