KDP EPUB Errors: What Each Error Means and How to Fix It
KDP EPUB errors can stop your upload entirely or quietly degrade your book's quality on Kindle devices. The problem is that KDP's error messages are often vague — "content error" or "structure issue" doesn't tell you which file, which line, or what actually went wrong.
This guide breaks down every major category of KDP EPUB error, shows you what the actual error messages look like, explains what each one means, and walks you through fixing each type before your next upload.
The Difference Between Hard Errors and Warnings
KDP separates feedback into two categories, and the difference matters for how urgently you need to act.
Hard errors block publication entirely. Your book will not go live until you fix them and re-upload a corrected file. These include missing TOC, invalid mimetype, corrupt file structure, and certain metadata problems. KDP usually shows these within minutes of upload.
Warnings don't block publication, but they degrade the reading experience. Deprecated HTML tags, unsupported CSS, and image sizing issues fall into this category. KDP will publish the book, but readers may see formatting problems on certain Kindle devices — particularly older e-ink hardware.
Fix hard errors first, then address warnings systematically, starting with those most likely to affect visible formatting.
Hard Error: Invalid EPUB Package Structure
KDP error message:
"Your file could not be uploaded. The file format is invalid
or the file is corrupt. Please check that you have uploaded
the correct file type."
"The file structure of your EPUB is invalid. The mimetype
file is missing or incorrectly compressed."This error means KDP can't read the basic structure of your EPUB. The ZIP archive that makes up an EPUB has strict requirements. Common causes:
- The
mimetypefile is missing, compressed, or not the first file in the archive META-INF/container.xmlis missing or points to a non-existent OPF file- The EPUB was zipped incorrectly — the top-level folder was included in the ZIP instead of just the contents
Fix: Unzip your EPUB, verify the structure, and repackage. The mimetype file must be added first using the store (no compression) method. Most standard ZIP tools compress it by default, which breaks the EPUB. Use an EPUB-aware packaging tool, or use a command-line zip tool with explicit compression flags.
Hard Error: Missing or Invalid TOC
KDP error message:
"No table of contents (TOC) found. Please include a TOC
in your file to help readers navigate your book."
"Unable to parse navigation document. The TOC structure
in your EPUB file is not valid."Your EPUB needs either an NCX file (EPUB 2.0) or a nav document (EPUB 3.0) with valid chapter links. If both are missing, or if the links inside the TOC file point to files that don't exist, KDP blocks the upload or publishes with a non-functional TOC.
Fix: Run your file through the EPUB Validator to see exactly which TOC element is missing or broken. The TOC Generator can rebuild a valid table of contents from your chapter headings if yours is missing or irreparably broken. After fixing, make sure the TOC file is correctly listed in the OPF manifest with the right media type and properties attribute.
Hard Error: Malformed OPF Manifest
KDP error message:
"Your book file contains errors. One or more files referenced
in the manifest do not exist."
"The OPF spine references an item ID that is not defined
in the manifest."The OPF file lists every component of your EPUB. If a file in the manifest doesn't exist, or a file that exists isn't in the manifest, KDP flags it as a structural error. Spine references that don't match manifest IDs cause the same problem.
Fix: Open your OPF file in a text editor and compare the manifest item list against the actual files in your EPUB folder. Remove manifest entries for files that don't exist. Add entries for files that exist but aren't listed. Make sure every file path uses the correct relative path and exact filename (case-sensitive).
Hard Error: Invalid XML in Chapter Files
KDP error message:
"Your book could not be published because one or more content
files contain invalid XML. Please check your XHTML files
for unclosed tags or improperly escaped characters."
"Parse error in chapter02.xhtml at line 143: element 'img'
must be closed."EPUB chapter files must be valid XHTML — strict XML. Common XML violations:
- Using bare
&in text content (must be&) - Unclosed
<img>tags (must be<img .../>or<img></img>) - Smart quotes or em dashes not encoded as UTF-8
- HTML comments containing double dashes (
<!-- -- -->is invalid XML) - Attribute values without quotes:
<p align=center>instead of<p align="center">
Fix: Run your EPUB through the EPUB Validator. It gives you a specific list of XML errors by filename and line number. Fix each one in a text editor. If the errors are widespread across dozens of files, a full rebuild using the Full Manuscript Mode is faster than patching hundreds of individual errors manually.
Warning: Unsupported CSS Properties
KDP warning message:
"Your book contains CSS properties that are not supported
by Kindle. Unsupported styles will be ignored and may
affect the visual appearance of your book."Kindle devices don't support all CSS. Properties like text-shadow, border-radius, box-shadow, certain flexbox properties, position: fixed, and CSS animations are ignored on older Kindle hardware. The book publishes, but those styles don't render — which may shift your layout significantly.
Fix: Review KDP's current Kindle supported CSS list and remove or replace unsupported properties. Use fallback-safe CSS: padding instead of box-shadow for visual separation, margin instead of position-based layout, and font-style: italic instead of any CSS animation for emphasis.
Warning: Deprecated HTML Tags
KDP warning message:
"Your book uses deprecated HTML elements that may not render
correctly on all Kindle devices. Consider replacing <font>,
<center>, and <b> with CSS equivalents."Tags like <font>, <center>, <s> (strikethrough), and presentational uses of <b> and <i> generate warnings. These tags work on most devices but are deprecated in HTML5 and may break on future Kindle firmware updates.
Fix: Replace deprecated tags with semantic alternatives and CSS. Use <strong> and <em> for emphasis, apply text alignment through your CSS file, and handle any strikethrough with <span style="text-decoration: line-through">.
Warning: Image Resolution or Size Issues
KDP warning message:
"Some images in your book may not display well on Kindle
screens. We recommend using images at 96 DPI for optimal
display on e-ink screens."
"Your book file is large. Consider reducing image sizes
to improve download performance for readers."KDP recommends 96 DPI for interior images and a minimum of 1600px on the longest side for covers. High-resolution print images (300 DPI) make your EPUB very large without improving screen quality. Oversized images also cause longer download times and may slow page rendering on older Kindle devices.
Fix: Resize interior images to 96 DPI and compress them before embedding. For covers: minimum 1600x2560px, JPEG at 85% quality is the right target. Use the Cover Checker to verify your cover meets all platform requirements before embedding or uploading separately.
How to Audit Your EPUB Before Every Upload
Run every EPUB through the EPUB Validator before uploading anywhere. The validator checks structure, OPF, TOC, HTML validity, image references, and CSS compliance — giving you a prioritized list of what to fix, separated into errors and warnings.
If you're formatting from a Word document, run it through the Word Cleanup Checker first. It catches formatting problems at the manuscript level — double spaces, inline styles, stacked blank paragraphs — before they become EPUB errors during conversion. Fixing at the manuscript level is always faster than patching after conversion.
Pro Tips
- Fix all errors before each re-upload. Don't upload again until your validator shows zero errors. Repeated failed uploads on the same title can slow your KDP review queue.
- Save your validation report. Before making any fixes, save the full validator report. If you introduce a new error while fixing an existing one, the saved report tells you what was there before versus what's new.
- Test the final EPUB in Kindle Previewer. After validation passes, open the file in Kindle Previewer and check the visual formatting, TOC menu, and image display on at least two device types (phone and e-ink reader). Validation catches structural errors; Previewer catches visual formatting problems.
- Keep your source manuscript clean. Most EPUB errors originate in the source document. Clean manuscripts produce clean EPUBs. Run the Word Cleanup Checker on every manuscript before any conversion step.
Frequently Asked Questions
How long does KDP take to process an EPUB after upload?
Structural errors are flagged within minutes of upload. If you get an error within the first few minutes, it's a structural or format problem you need to fix before the file enters content review. Content review — for policy compliance — takes 24–72 hours. A book that passes structural validation enters content review automatically; you don't need to resubmit once structural errors are fixed.
Can I fix EPUB errors without specialized software?
Yes. Most EPUB errors can be fixed in any text editor. EPUB files are ZIP archives containing HTML, CSS, and XML files. Unzip the file, fix the error in the relevant file using a text editor, repackage correctly, and you're done. The challenge is knowing which file to edit and exactly what to change — which is exactly what a validator report tells you, with filename and line number precision.
Will fixing errors on an already-published book affect sales or ranking?
No. Uploading a corrected version doesn't affect your book's sales history, reviews, or search ranking. Readers who already bought it get the updated file automatically via Whispersync. The update typically propagates to devices within 24–48 hours. You can update as many times as you need without any ranking penalty.
Does KDP have a limit on how many times I can re-upload?
There's no published hard limit on re-uploads, but frequent failed uploads on the same ASIN can slow your review processing time. Fix all known errors before each attempt rather than uploading one fix at a time and checking if KDP accepts it. Run the validator, fix everything the report shows, then upload once.
Is there a difference between EPUB technical errors and KDP content policy violations?
Yes, and the timeline is different. EPUB technical errors are flagged within minutes of upload — they prevent the file from entering the publishing pipeline. Content policy violations (prohibited content, copyright issues, misleading metadata) are flagged after the file is structurally accepted, during the 24–72 hour content review. If your rejection arrived in under 10 minutes, it's a technical problem. If it arrived after a day or more, it's a content issue and requires a different kind of fix.