Free EPUB Checker

How to use the EPUB checker

Drop your .epub file onto the box. The checker opens it in your browser and lists anything stores are likely to reject, with what to fix. Nothing is uploaded, so it’s safe for unpublished books.

What it checks

An EPUB is a ZIP archive with a fixed structure. The EPUB standard requires a few things that stores check first:

• The mimetype file must be the first file in the archive, uncompressed, reading exactly application/epub+zip. Zipping a folder by hand usually breaks this.
• The container and package files (META-INF/container.xml and the .opf file) must exist and point to each other.
• Metadata: a title, a language, a unique identifier and, for EPUB 3, a last-modified date.
• Every file listed in the package must be in the archive, and the reading order must only use listed files.
• A table of contents: a navigation document for EPUB 3, or an NCX file for EPUB 2.
• Pages must be well-formed XHTML, with working internal links and images inside the book.

It also flags things that cause trouble in stores: a missing or small cover, images without alt text, DRM encryption, and files near KDP’s 650 MB limit. Each store then runs its own checks on upload; our guide to publishing a book on Kobo shows where that happens on Kobo Writing Life.

This covers the problems that stop most uploads, but it isn’t a full validation. Apple Books requires books to pass EPUBCheck, the official validator, so run it before you submit there. No EPUB yet? Make one from Word, PDF or Markdown.