Happy Smile Sudoku quickly solves all sudokus with only 1 solution. If there are more than 1 solution Happy Smile Sudoku displays 1 of these solutions together with a message that says the more than 1 solution have been found .
The program can also create new sudokus without a symmetry or with a symmetry among the 4 symmetries most often found in newspapers. These 4 symmetries are either the rotation or mirroring of the positions, where there are a number in the top or the top left of the sudoku board, to the rest of the sudoku board. The generated sudoku will then have clues only in these positions. It is also possible to define all the positions where the generated sudoku shall have a clue. This is done by defining what is called a template. Furthermore it is possible to influence the difficulty of the sudokus the program generates, from the easy to the very hard difficulty level. In the free version 50 sudoku numbers are available when creating a new sudoku, but each sudoku number can be used to create an enormous amount of different sudokus, because most templates can generate 50 different sudokus. In the registered version 100.000 billion sudoku numbers are available, making it easier to create different sudokus.
When solving a generated soduko oneself the program can display hint to help solving them
It is possible to choose the color of various things being displayed, from the color of the board to the color of the suggestions the program can display in helping to solve a sudoku.
Putting numbers onto the board when solving a sudoku or when defining a template for the positions in a new sudoku puzzle is as easy as dragging and dropping numbers onto, around on or off the sudoku board.