Interior: bring your manuscript
Start a book with a title, your name and a genre, and it suggests the usual trim size for that genre. Then bring your manuscript as a .docx straight from Word. Before it formats anything, it reads the file and tells you what it found: words, chapters, and anything to fix.
Then it typesets the whole book the way a publisher sets a novel, a paragraph at a time, and grades its own work in plain words: how many pages fill to the bottom, rivers of white space, facing pages that end together. When a page runs short, it tells you how many words would fill it. See the difference it makes.
You get: a print-ready interior PDF, checked before it downloads.