Actually the whole sprite section is not very clear on how to use.
1) Sprite loading-
Please change the bar used to a load sprite from Sprite None to Load Sprite and then, once loaded, show the name of the sprite in that box. Currently it shows the first value inputted which is not very useful to most people I believe.
When you click on the sprite bar that says none it will pop and say "Input frame width" etc.
Considering this is made in Gamemaker couldn't you load in the texture/image and try something like sprite_get_width(index); or something like 1/texture_get_texel_width()? It's been a long time since I've worked on a gamemaker project...
It would also be nice if I could adjust the size of that image later without reimporting the sprite.
2) Tab color sizes are wrong.
Although looking at your online documentation it looks like that might be some sort of style you are going for... I'm not sure.
3) When you click on one of the categories it should auto select the 1st sub category.
For example when you select Basic then Ding Bang should show as selected. I personally don't think the association is very clear.
It's a little confusing to deal with the sprite selection because it doesn't show what I selected and I had to figure out there were main categorizes and subcategories. Also it's not clear if the sprite I loaded can be saved into a category.
4) It would be really nice if I could store my own sprites in a separate category. Gamemaker once made it easy to create a directory and store saved assets and reload them but I'm not sure if they have removed those features since I last used it. It's a request, but a minor one.
5) Oh and I think ran into an issue using the timeline play button below and the regular play button.
Earlier I loaded a sprite with dimensions bigger than the sprite so that might have caused the problem, but I switched to some ding bat before I hit play. I'm not sure which ding bat, as it's not clear what you clicked on since there is no highlighting or selector.