Click or tap on the Sudoku to select a cell, then use the keyboard or the pop-up menu to set the value of that cell; closing the pop-up or hitting "Delete" or "Backspace" keys will remove the value. Once a value is set in a particular sub-grid, horizontal, or vertical, you won't be able to choose that value for other cells in those sub-grids / horizontals / verticals. All other checks are performed after you hit the "Solve!" button.

Once you are satisfied with the state of your Sudoku, press "Solve!" and you will see the solver do its magic. While properly formed Sudoku should have exactly one solution, it is possible that either no solutions are found, or many exist. The solver will inform you when no solutions exist and will let you examine the many solutions when more than one exists.

When the solver finds a solution you can also hover / tap over the Sudoku, to confirm that the original values are still set as before, and that each sub-grid / horizontal / vertical has unique values, as it should.

The Sudoku solver is intentionally throttled down, as for most puzzles it still only takes a few seconds to run, and, in my opinion, is fun to watch. However, on harder puzzles the solver can take a few minutes to reach a solution with the default behavior. If you don't want to wait, and just want to get the solution as fast as possible, click here to open the solver with the fast mode enabled in a new window.

You can share a partially-filled puzzle either by clicking the button above (right next to the "?"), or simply by copying the URL, which is exactly what that share button does.

I've included a couple of links below, feel free to reach out to me with ideas, suggestions or other feedback.