2026-06-18 · all guides

KDP Previewer Errors and How to Fix Each One

Why the previewer rejects files

When you upload a manuscript or cover, KDP runs automated checks before a human ever sees the book, and the online previewer is where the results appear. The checks exist because print is unforgiving: a margin problem that looks trivial on screen becomes text swallowed by the binding on paper. The three errors that account for most failed paperback uploads are text or images inside the gutter margin, images below 300 dpi print resolution, and a cover that does not match the book, either in dimensions or in the title and author text Amazon reads off it.

The previewer distinguishes between errors, which block publishing until fixed, and warnings, which let you proceed at your own risk. Treat warnings seriously anyway. A low-resolution image warning means blurry printing, and a blurry book earns returns and one-star reviews even though Amazon let it through.

Gutter and margin errors

The gutter is the extra inner margin on the binding side, and KDP scales its requirement with page count: 0.375 inches up to 150 pages, 0.5 inches for 151 to 300 pages, 0.625 inches for 301 to 500, and 0.75 inches for 501 to 700. The previewer error "text in the gutter" or "content in the margin" means something, often a page number, header, or wide table, crosses into that protected zone. Because the gutter alternates sides on odd and even pages, your document needs mirrored margins, not symmetric ones.

The fix is in your source document, not in KDP: set inside margins to the required gutter plus your base margin, enable mirror margins, and re-export the PDF. If the error appears only on a few pages, look for elements that ignore margins, like full-width images or manually positioned text boxes. Then re-upload; the previewer re-checks the new file from scratch.

Low-resolution image warnings

Print requires 300 dpi at the physical size the image occupies on the page. A 600-pixel-wide image stretched across a 6-inch page is only 100 dpi, and the previewer will flag it. The confusion is that dpi is not a property of the image alone but of the image relative to its printed size: the same file is fine at 2 inches wide and flagged at 6. Screenshots and web images are the usual offenders because they are built for 72 to 96 dpi screens.

You have two honest fixes: source a higher-resolution version of the image, or print it smaller. Upscaling in an editor adds pixels but not detail, and while it may silence the warning, the print will still look soft. For covers, KDP wants 300 dpi at full wrap size, which for a 6 by 9 paperback means a file several thousand pixels on each side. Build covers at print size from the start rather than scaling up a thumbnail.

Cover mismatch and spine problems

A cover mismatch error means the cover file disagrees with the book: wrong dimensions for the trim size and page count, or cover text that does not match the metadata. The wrap cover for a paperback must be sized to an exact spine width, calculated as page count times 0.002252 inches for white paper or 0.0025 for cream. Change your page count by even ten pages and the old cover no longer fits; the previewer will show spine text drifting onto the front or back.

Fix it by regenerating the cover at the correct dimensions using the KDP cover calculator and template for your final page count. Also check that title and author on the cover exactly match the details page, since discrepancies get flagged in review even when the previewer passes them. If you would rather never do this math, tools that generate the interior and cover together keep them in sync automatically. ebookdone computes the gutter and spine from your final page count and outputs both files matched, with a free preview at /new.

A pre-upload checklist

Most previewer failures are preventable with a five-minute check before upload. Confirm your trim size matches what you will select in KDP. Confirm mirror margins with the correct gutter for your page count. Confirm every image is 300 dpi at its printed size. Confirm the cover wrap is sized for your exact final page count and paper color, and that the cover text matches your metadata word for word.

When the previewer does flag something, fix the source file and re-export rather than trying to patch the PDF. Each new upload gets a full re-check, and there is no penalty for uploading multiple times before you publish. The previewer is annoying precisely because it catches things that would otherwise become printed defects in a customer’s hands.

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