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"Your expected cover size is X but the submitted file size is Y." "Insufficient gutter." "You chose 6" by 9" trim size, but your interior file was submitted at…" Drop your PDFs in below and see which page fails, by how many inches, and what to change — then rebuild the file at the correct size.
Match these to what you selected in KDP. Wrong settings here means wrong results.
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Set your trim size and bleed on the left, then drop in your interior PDF. Add the cover too and you'll get spine width, barcode clearance, a full book preview and a corrected file to download.
File setup is fiddly work — bleed, gutter, spine width, image resolution and colour profiles all have to line up before KDP accepts anything. We handle it as part of every illustration project, or as a standalone formatting job if your artwork is already done.
Get Your Files Fixed → or see pricingThe most common upload rejection, and almost always a spine-width problem rather than anything wrong with your artwork. KDP recalculates the spine from your page count and paper type, then expects the whole wrap to match. Ranked by how often each cause turns up: the paper type at upload doesn't match what the designer used — cream stock is thicker than white, so the spine and the entire cover get wider; the page count changed after the cover was built and nobody told the designer; or the wrong trim size was selected at upload. Covers are checked tightly — authors report rejections over gaps as small as 0.077", so "close enough" isn't. Upload your cover above and you'll get the exact expected figure with the spine broken out, so you know which number to hand back to your designer.
Something sits inside the inside margin — the strip nearest the binding, which physically disappears into the spine when the book is bound. The requirement scales with thickness: 0.375" up to 150 pages, 0.5" for 151–300, 0.625" for 301–500, 0.75" for 501–700 and 0.875" above that. Outside, top and bottom need 0.25", or 0.375" on a bleed file. The checker reads your PDF's real text layer and marks every run that crosses the line, on the exact page, with the gutter on the correct side — left for odd right-hand pages, right for even left-hand pages.
Your PDF page size doesn't match the trim you picked. With bleed there are two sizes KDP accepts, which trips up a lot of people: 6.125 × 9.25" is the documented spec, with bleed on the top, bottom and outside edge only, while 6.25 × 9.25" adds bleed to all four sides. Most design software exports the second, and KDP centres and trims it without complaint. This tool recognises both, so you don't get a false alarm — and because interiors are centred rather than measured to the millimetre, a difference under a sixteenth of an inch is reported as fine rather than as an error. Anything genuinely off, including files exported with crop marks, gets flagged with the exact gap.
Your artwork stops at the trim line instead of running past it. When the printed sheet is cut, the blade drifts by up to a sixteenth of an inch, and a white sliver appears along the edge. The checker samples the pixels along every edge of each page and tells you which specific edges come up short — so you're not guessing which side to extend.
Very. Covers are measured against a calculated wrap and rejected over small fractions of an inch. Interiors are more forgiving because KDP centres and trims them, which is why this tool treats the two differently instead of applying one blanket rule.
300 DPI at final printed size. Below about 200 DPI a full-page illustration goes visibly soft; below 150 DPI it looks blocky, and no amount of upscaling recovers detail that was never captured. Because effective resolution is pixel width divided by printed inches, an 8.5" wide page needs artwork around 2550px wide — scaling a smaller file up to fill the page is exactly what causes the problem.
No. Everything runs in your browser using JavaScript — the analysis, the preview and the corrected PDF. Nothing is transmitted, stored or seen by anyone. You can disconnect from the internet after the page loads and it still works.