What it does
Once every page in a 24–300 art-page book (up to 150 when single-sided, since each page gets a blank back) has been generated, the PDF builder assembles the file KDP expects instead of leaving that step to you. Single-sided books add a blank back page for every art page — mainly so marker and felt-tip ink does not bleed through to the next drawing — which is why a single-sided book needs twice the paper of the same art count printed double-sided, where art sits front and back on the same sheet. The builder sets the gutter margin from the resulting interior page count and confirms the book clears every print check before the download button unlocks.
| Interior page count | Gutter margin |
|---|---|
| Up to 150 pages | 0.375 in |
| 151–300 pages | 0.5 in |
| Setting | Effect on the PDF |
|---|---|
| Single-sided | Each art page is followed by a blank page (up to 150 art pages, 300 interior pages) |
| Double-sided | Art printed front and back, halving paper use for the same art-page count (up to 300 art pages, 300 interior pages) |
| Outer safe margin | 0.375 in kept clear on the non-gutter edges of every page |
From Forest Friends (Kids) · Make one like it
The check that runs before download
Six checks run before the download button unlocks: all pages ready with none failed, every page 1-bit (no gray pixels), interior page count inside CrayonMill's supported 24–300 window (KDP itself allows more), gutter set correctly for that count, the outer safe margin, and resolution. There is no "page order" check — pages print in the order they were generated, and the six checks above are what has to pass. The checks read the book's current status (how many pages are ready, how many failed) rather than opening the assembled PDF file, so they update the moment a page's status changes. If any check fails, the button stays disabled and the check names its own numbers — for example "38 / 40 ready" — but it will not point at a specific page; the library grid is where a failed page shows up visually so you know which one to regenerate.
What it does not do
- It does not build the cover file. This tool assembles the interior PDF only; cover dimensions are a separate step covered in the cover size guide.
- It does not let you skip a failing check "just this once" — the button will not unlock until every page passes, even if you are confident a borderline page is fine.
- It does not support trim sizes other than 8.5 × 11 in yet, so a book planned for a different trim needs a different workflow for now.
- It does not identify a failing page by number inside the check itself — that comes from the library grid, not the preflight summary.
Sources
Last verified 2026-09-04. Updated 2026-09-04.