Whether you already have an EPUB or are simply learning what comes next, this guide walks you through the checks that help a book upload cleanly and read well: book information, chapter order, contents links, images, and the reading experience.
Start with the EPUB you may upload
If you already have an EPUB, check the exact file you may send to a bookstore, library, or distributor. It does not matter which writing or formatting tool created it.
If you do not have an EPUB yet, that is perfectly fine. Use this page to learn what you will need to check once your file is ready.
If you later change the book or the settings used to create it, check the new EPUB again. A report for an older file does not tell you whether the new one is ready.
Check the file with EPUBCheck
EPUBCheck is the official tool for checking whether an EPUB follows the EPUB standard. It looks for missing files, broken links, incomplete book information, navigation problems, and other issues that may cause an upload or reading problem.
1. Follow the official EPUBCheck instructions to install or open the tool.
2. Open Terminal on a Mac or Command Prompt on Windows, then go to the folder that contains your EPUB.
3. If your installation includes the epubcheck command, run epubcheck your-book.epub.
4. If you downloaded the Java version, run java -jar /path/to/epubcheck.jar your-book.epub instead.
5. If you want to save the results in a separate file, run epubcheck --json report.json your-book.epub.
Keep the report beside the EPUB you checked. That makes it much easier to remember which results belong to which file.
Start with the most important messages
EPUBCheck labels its most serious messages FATAL or ERROR. Start there, because those messages mean the file is broken or does not meet a required rule. Review WARN messages too, but remember that a warning may describe a possible risk rather than a guaranteed failure.
Most messages name the part of the EPUB that caused the problem and may include a line number. Write that down before making changes so you can connect the message to the right chapter, book-information field, link, image, or style.
Do not dismiss a message just to reach zero warnings. First understand what it affects and whether a reader, bookstore, or library platform could notice the problem.
Fix the original content, then check the new EPUB
Whenever possible, make the correction in the original manuscript, book information, or settings used to create the EPUB. Editing the files hidden inside an EPUB may fix the immediate problem while leaving the original version ready to create it again later.
Create a new EPUB with the tool you already use, then run EPUBCheck on that new file. Keep the old report as a record of what changed, but do not treat it as proof that the new file passes.
Repeat these steps until you understand every remaining message and the EPUB meets the requirements of the bookstore, library, or reading app you plan to support.
Open the EPUB in more than one reading app
EPUBCheck can find technical problems, but it cannot tell you whether a chapter opening looks balanced, an image is comfortable to view, the text is pleasant to read, or the book works well on a small screen.
Open the same EPUB in the previewer offered by your intended bookstore when one is available. Then open it in at least one separate EPUB reading app.
In each reader, click every table-of-contents entry, follow internal links, inspect images, change the font size, move between chapters, and check the transition from the final chapter into back matter.
Helpful Examples and Comparisons
Common EPUBCheck messages and what to do
The exact message may vary. Use the file name and location in the report to find the part of the book that needs attention.
Type of message
What it usually means
Where to look
What to do next
The EPUB file itself
A required file is missing, damaged, or stored incorrectly inside the EPUB.
The tool or service that created the EPUB
Create the EPUB again with a tool that supports the current EPUB standard.
Book information
A required title, language, book identifier, list of included files, or reading-order setting is missing or incorrect.
Your book details or the settings used to create the EPUB
Correct the responsible field or setting, then create a new EPUB.
Contents and navigation
The contents list, a chapter destination, or part of the reading order is missing or broken.
Chapter headings, contents settings, or link destinations
Repair the book structure, then click every destination in a reading app.
Chapter content
A chapter contains invalid structure, repeated IDs, or missing language information.
The original chapter or the template used to create it
Correct the original content or template instead of simply hiding the message.
Links, images, fonts, or styles
The EPUB cannot find something it needs, such as an image, a font, a style file, or the destination of a link.
The original image, font, style, or link
Restore or remove the missing item, create a new EPUB, and check it in a reader.
A warning or helpful notice
The EPUB may still be valid, but something could cause a compatibility or reading problem.
The feature named in the message
Understand the warning, write down why it is acceptable if you keep it, and test that part in more than one reader.
What each kind of check can tell you
Check
What it can find
What it cannot tell you
You are ready when…
EPUBCheck
Missing files, incomplete book information, broken navigation, invalid chapter structure, and missing links or images.
Whether the design feels polished, the text is comfortable to read, or a specific bookstore displays it beautifully.
FATAL and ERROR messages are fixed, and you understand every warning that remains.
Your bookstore’s previewer
How that bookstore displays the contents list, images, styles, and chapter breaks.
How the book behaves in other reading apps.
You can comfortably read and move through the whole book in the previewer.
A separate EPUB reading app
Differences in text flow, fonts, spacing, images, links, and navigation.
How the book behaves on every possible device or platform.
The book remains easy to use after you change the font size and move around normally.
A manual contents and link check
Links that go to the wrong place, old chapter labels, and awkward jumps near the end of the book.
Hidden technical problems that require EPUBCheck.
Every contents entry and important link takes you to the right place.
Where to open and test your EPUB
You do not need every app listed here. A good minimum is your intended bookstore’s previewer plus one separate EPUB reading app.
App or previewer
Why it helps
What to try
It looks good when…
Your bookstore’s previewer, such as Kindle Previewer
Shows how the bookstore where you plan to publish displays the file.
The contents list, chapter starts, images, links, font-size changes, and the move into the ending sections.
The whole book is easy to read and every important link works.
Thorium Reader on desktop
Gives you a free, independent EPUB reader for a second opinion.
Contents links, themes, larger text, image sizing, and keyboard navigation.
Everything stays in order and remains easy to use after you change the display settings.
Apple Books on a Mac, iPhone, or iPad, if one is available
Adds another popular reading app and, on an iPhone or iPad, a useful small-screen check.
Contents links, text size, screen rotation, images, and the sections after the main book.
Nothing disappears, overlaps, or becomes difficult to reach at normal reading settings.
Another bookstore or library platform you plan to support
Helps you catch differences that only appear on that particular platform.
The upload preview, chapter labels, cover, book information, and a few chapters from different parts of the book.
The platform accepts the file and shows the book in the right order.
Before You Publish
If you already have an EPUB, set aside the exact file you may upload.
If you do not have one yet, save this checklist for when your EPUB is ready.
Run EPUBCheck on the EPUB and save the report.
Fix every FATAL and ERROR message before treating the file as ready to distribute.
Read each warning and note which file and location it points to.
Confirm the title, author name, language, book identifier, chapter order, and contents links.
Whenever possible, fix problems in the original manuscript, book information, or settings used to create the EPUB.
Create and check a new EPUB after every correction.
Open that same file in your bookstore’s previewer when one is available.
Test it in at least one separate EPUB reading app too.
Click every table-of-contents entry and important link, then check the move from the final chapter into the ending sections.
Upload only the EPUB that completed both EPUBCheck and your reading-app tests.
If You Find a Problem
EPUBCheck says the table of contents or navigation is missing
What to change: Check the chapter headings in the original book, then create a new EPUB with a complete contents list.
Check again: EPUBCheck no longer reports missing or invalid navigation.
A table-of-contents entry opens the wrong chapter
What to change: Look for repeated chapter headings or links that point to the wrong place, then create the EPUB again.
Check again: Every contents link opens the chapter you expect.
EPUBCheck finds two link destinations with the same hidden label (ID)
What to change: Make sure every chapter and major section has its own unique link destination in the original content.
Check again: EPUBCheck no longer reports a repeated hidden label or ID.
A link inside the book is broken
What to change: Correct the link in the opening pages, ending pages, or chapter where it appears.
Check again: The link works when you click it in a reading app.
EPUBCheck finds a problem with the book information
What to change: Correct the title, author, language, or book identifier before creating the EPUB again.
Check again: EPUBCheck no longer reports a required book-information error.
EPUBCheck warns about styling that may not work everywhere
What to change: Simplify the styling that caused the message, especially if it affects readability.
Check again: The warning is resolved or understood, and the page still looks good in at least two readers.
The chapters are in the right order, but the contents list is out of date
What to change: Rebuild the contents list from the current chapter headings before creating the EPUB again.
Check again: The contents list and chapter order now match.
The same message appears after you fix the problem
What to change: Make sure EPUBCheck is checking the new file you created after the fix, not an older copy with a similar name.
Check again: The report belongs to the new EPUB and shows the result of your correction.
Want to organize the book in Senswriter?
These steps work no matter which writing or formatting tool you use. Senswriter is simply an option if you would like one place to organize a manuscript and prepare it for publication.
Create a free account to start a manuscript or import work you already have.
Organize chapters, scenes, opening pages, and ending pages with a free account.
Preview the book as you prepare it for print and ebook release.
If you later need final files, review the paid export options and decide whether one fits your needs.
Is EPUB validation still needed if the file opens in a reader?
Yes. A file can open on your computer and still be rejected when you upload it.
Should I edit EPUB files directly to fix warnings?
Usually no. Make the change in the original book or its settings, then create the EPUB again so the same problem does not return later.
When should I rerun EPUB validation?
Check it again after any meaningful change to the writing, chapter order, book information, or opening and ending sections.
What are the most important EPUB checks before upload?
Run EPUBCheck, click every table-of-contents link, and test the same file in your bookstore’s previewer plus at least one separate EPUB reading app.
Can I ignore book-information warnings if the pages look fine?
No. Problems with the title, author name, language, or book identifier can still cause an upload problem even when the pages look normal.
Why not open the EPUB and edit its files directly?
Those changes are easy to lose the next time you create the EPUB. Fixing the original manuscript, book information, or settings is more reliable for future revisions.
Can I use this guide if I do not use Senswriter?
Yes. These EPUBCheck and reading-app steps work with EPUB files created by any writing, formatting, or conversion tool. Senswriter is simply an option if you later want one place for organizing a manuscript and preparing it for publication.