Rebrickable Lost Parts bulk entry

Say you’ve been donated a box of Lego, and some manuals, which sort of make up some sets but probably none complete. Before donating them onwards, you’d like to sort them out and complete them if possible, perhaps buying any missing parts. To do this on Rebrickable, it appears you have to add the set to your collection, then go through and mark every missing part one by one, taking a good number of clicks for each part (click on part, click on Lost Parts, enter number, click save, close part, repeat). So I made this, which will add multiple things to your Lost Parts at once, remember where you’ve got to if you refresh, and make the process a lot smoother. Make sure you’ve added the set to a list first, and then: