1. each column
2. each row
3. each of the nine 3x3 sub-grids (also called "boxes" or sub-squares")

contains all of the digits from 1 to 9.

The puzzle has been provided a partially completed grid, which has a unique solution. Please fill in the missing digits. With checkbox "check" you may control a check for correct input. If checked, correct digits will then be shown in green color, wrong digits wil be painted in red color. If checkbox "help" has been selected, all currently possible number-candidates will be shown in each cell of the grid.

You can also create your own Sudoku puzzle. An empty playing field is provided via the selection "own Sudoku" and "new Sudoku", in which you can then enter the numbers (at least 17) for a new puzzle.

Sudoku puzzles are designed to be solved by human players with pencil and paper but with well defined algorithms, it is possible to be solved in almost real time by computer or even smartphone. A standard Sudoku puzzle contains 81 grids which consists 9 grid rows and 9 grid columns. Sudoku have 9 non-overlapping zones (sub-squares), which each zones consists of 3 grid rows and 3 grid columns. In each zones, there can be only a number occurring only once in each grid. Players may use a wide range of strategies which deals the solutions either from zones or the whole grid.

More details about Sudoku and common strategies to solve Sudoku puzzles will be found at  Wikipedia .