Fill the grid so every row, every column and every three by three box holds the numbers one to nine exactly once.
A new puzzle every day at five difficulties, from one you can do over coffee to one that will take the evening.
Click a square and type a number, or pick one from the pad. Anything already in that square's row, column or box is not allowed there.
If only one number is legal in a square, that is the answer. If a number can only go in one square of a row, column or box, it goes there even if that square had other options.
Use the pencil to leave small candidate marks when a square has two or three possibilities, then watch them disappear as the grid fills.
The hint button explains a step rather than just filling a square, so it is worth using when you are stuck rather than starting again.
No. The nine symbols could be colours or letters and nothing would change. It is a puzzle about where things can and cannot go.
Yes. Every puzzle here is checked for a single solution before it is published, so two numbers that both seem to fit means an earlier entry is wrong.
No. Each puzzle can be finished by reasoning alone at the difficulty it is set, which is what the difficulty actually measures.
Yes. The calendar button opens the previous days, and your progress on each one is saved separately.
Sudoku arrived in newspapers in the early 2000s and never really left, because it is the rare puzzle that is genuinely the same for everyone: no vocabulary, no trivia, nothing but the grid in front of you.
The technique that gets you furthest is scanning by number. Take the sevens, look at each box that still needs one, and find the boxes with only one legal home for it.
When scanning dries up, go looking for pairs. Two squares in the same unit that can only hold the same two numbers lock those numbers away from everything else in that unit.