This puzzle tries to fill the screen space you give it, so you can resize your browser window to make it bigger or smaller as you want. To fill in a number that you definitely know, use your mouse to left-click on the square and select the number. If you're not sure but want to mark a possibility (for example, the 2 can either be here or here), then right-click on the square instead and select the number. This possibility will be written smaller and grey in the corner of the square, like a pencil mark to remind you.
The code running here is from the ActivityWorkshop, and the numbers were generated using the free (GPL'd) software
This example is coded as
N1-059 which means only level 1 rules are needed to solve it, and it starts with 59
empty squares. Later puzzles will get harder, to give you a challenge once you've solved this one!