The number puzzle on squared paper: a 9×9 grid, some digits already written in, and one rule. Every row, every column and every 3×3 box must hold each digit from 1 to 9 exactly once. Free in your browser, at four levels, alone or racing a friend.
There is no arithmetic in sudoku: the digits could as well be letters or colours. It is all elimination. A 7 in a row rules out every other cell of that row, of its column and of its box, and the puzzle is solved by seeing where the only place left for a digit is, or the only digit left for a place.
Every puzzle here is dealt fresh and checked before you see it: it has exactly one answer, and you can always reach it by logic, without guessing. The level says which techniques you will need:
The grid, the one rule, pencil notes, clashes, the four levels, and racing a friend.
Read the rules →The techniques that solve every puzzle here, from scanning for hidden singles to the X-wing and the swordfish.
How to solve sudoku: techniques →Racing a friend, you both get the same puzzle at the same moment, each on your own sheet. Fill it in first and you win. You see how much of their grid is filled, never what they wrote.