How to Check an EPUB File for Errors (Free Guide)

You've made an ebook. It opens on your computer and looks fine. But will it work in every store, and on every reader's device? An EPUB can look perfect in one app and break in another.

Checking your file before you publish saves you from rejected uploads and unhappy reviews. This guide shows you how. The quickest way is Ebook Medic, which checks your EPUB and explains any problems in plain words.

Why check at all?

An EPUB is a bundle of files: your chapters, pictures, cover and a few "map" files that hold it all together. Reading apps are often forgiving and will open a file even with mistakes inside. Book stores are stricter. A small mistake can mean:

Your upload is refused.
The table of contents doesn't work.
Pictures or the cover don't show.
Some chapters are missing on certain devices.

Method 1: Check with Ebook Medic (easiest)

Go to tools.ltd/ebook-medic.
Choose your EPUB file.
Wait a moment while it checks the file with the same rules as EPUBCheck. The check runs in your browser, so your book never leaves your device.
Read the list of problems, if any. Each one is explained simply.
If there are problems, Ebook Medic fixes what it safely can and checks the book again. You see both results for free.
Get the fixed file. Some problems need a person to fix, and Ebook Medic tells you which ones are left.

Method 2: EPUBCheck (free, technical)

EPUBCheck is the official free checker for EPUB files, made by the group that looks after the EPUB standard. It catches a lot, but:

It may need to be run from a command window on your computer.
The messages use technical words and line numbers.

If that's fine for you, it's a great tool. If not, Ebook Medic checks your book with the same rules and explains the results in plain language.

Method 3: Open it in more than one reader (free)

A checker finds technical errors. You also need to look at the book with your own eyes.

Open the EPUB in two or three different reading apps. Free options include Apple Books on Mac or iPhone, and Calibre's viewer on Windows or Mac.
Check the cover appears.
Click every item in the table of contents. Each should jump to the right place.
Look at pictures. Are they all there, and the right size?
Check special characters like quotation marks, dashes and accented letters.
Read the first and last pages of each chapter for formatting surprises.

If you plan to sell on Kindle, Amazon's free Kindle Previewer program shows how your book looks on Kindle devices.

What to do if you find errors

Note each problem and where it is.
Fix it at the source if you can. If you wrote the book in Word, Google Docs or a writing app, fix it there and export a new EPUB.
Or fix the EPUB directly. Ebook Medic can fix many common problems for you.
Check again. One fix can sometimes reveal another problem.
Keep a copy of each version, named clearly like "My Book v3."

A pre-publishing checklist

The file passes a checker with no errors
Cover shows in at least two reading apps
Every table of contents link works
All pictures appear
Title and author name are correct in the book details
No leftover notes, comments or highlights

Sharing drafts with others

If you're sending draft chapters or contracts to an editor or agent as PDFs, check them for private details first, like your home address or bank details on a contract. TrueRedact removes those from a PDF for real, right in your browser.

Common error codes, in plain words

EPUBCheck gives each problem a short code. These are the ones we see most.

RSC-005: "Error while parsing file." Read the words after it. That is the real problem. It might be a missing table of contents, a missing title or language, or a tag that isn't allowed.
RSC-016: A fatal error. Often it is a lone & sign in the text. It should be written as &.
RSC-001: The book's file list names a file that isn't there.
RSC-008: A file is in the book, but the file list leaves it out.
OPF-030: The book's ID number is missing or points to nothing.
PKG-006: The first file inside the EPUB must be a small file called "mimetype". It is missing or in the wrong place.

Ebook Medic fixes most of these on its own. It won't guess at your words. If a fix would mean changing your book's text, it tells you instead.

Frequently asked questions

My EPUB opens fine. Do I still need to check it?

Yes. Many reading apps hide small mistakes. Stores and other devices may not be so forgiving.

What is EPUBCheck?

EPUBCheck is the official free tool for checking EPUB files. It is very thorough but written for technical users.

How often should I check my file?

Every time you make a new version, even after a small change like fixing a typo.