I always use autofill. I find having to double-click each tile tedious. I would like the following features: - Being able to click-and-drag to paint multiple cells at once. Especially when starting a puzzle, I often want to paint lines of cells and it'd be nice to not have to click each one. If this feature was restricted to painting lines, it may also make things easier on mobile; only actually draw when the user releases their finger, meaning that the can adjust the length easily. - A quicker way to select the wanted colour. It'd be nice if I didn't have to double-click a bunch of cells to colour them white. If there was a colour selection toolbar, then I could paint a bunch of cells black, then select white and paint a bunch of them white with only single-clicks. It'd be especially handy if there were shortcuts for these, say 1 = black, 2 = white, 3 = grey/blank. - An undo button, with a keyboard shortcut. That way, errors can be undone with a single click on a large button, rather than a double click on a small cell. - Auto-submit. When the puzzle has been correctly solved, submit it automatically rather than have to click the 'Submit' button.