ePub (short for electronic publication) is a free and open standard for electronic publications. It was established by the International Digital Publishing Forum (IDPF).

epub is designed to adapt easily to a large number of computers, e-readers and screen sizes.

Although the ePub format is a standard, several variations in structure can make a ePub compliant or not with the criteria of the various distribution platforms for digital books. 

Publishers have a duty to require the highest possible quality in their ePubs, right from the beginning, to avoid problems and incompatibilities between different systems later on. To this end, here are some guidelines to help you create quality ePubs. Note that these are only recommendations, and your file will still be accepted on the platform even if it is not 100% compliant. Even if an ePub has errors for one partner, it may be totally fine for another.

Nevertheless, a good EPUB should:

  • Be structured according to the standard.
  • Pass the ePubcheck validation, in its latest version (currently 1.2). For more information, see this page. Online validation tools are also available, as here.
  • URIs (Uniform Resource Identifiers) ​​must properly encode non-alphanumeric characters.
  • All files in the EPUB should be listed in the manifest (OPF).
  • Only UTF-8 and UTF-16 encodings are allowed in EPUBs.
  • All the files in the EPUB must be legible and unlocked.
  • The cover must be solid colour without 3D effect, and must not show the edge of the book.
  • All images must be RGB (not CMYK).

Additional notes from a vendor guide to Kobo

  • Each chapter/section within the ePub is separated into its own html/xml file All chapters/sections are respectively referenced within the OPF file
  • The <manifest> section should reference all the individual files representing chapter/section content
  • The <spine> section should then take the chapters/sections in the <manifest>, and be ordered in the way you want it to appear from beginning to end All chapters/sections are clearly defined within the NCX file with its corresponding title
  • Each <navPoint>, which represents a chapter/section, should have a corresponding title
  • Each <navPoint> should reference an existing file within the ePub Each ePub file is sent with a corresponding cover image The ISBN for the book is labeled in various areas:
  • ePub Filename (eg. 9781234567890.epub)
  • OPF, in the <metadata> section within <dc:identifier> (<dc:identifier>9781234567890</dc:identifier>)
  • Cover image filename (eg. 9781234567890.jpg) Use decimal entities in favour of character entities (use " in favour of ") Text encoding should all be in UTF-8 (this can be checked in the OPF, the first line should be “<?xml version="1.0" encoding="UTF-8" ?>”


By following these simple rules, your EPUB will have a better chance of being approved for sale at many retailers, from independent booksellers to Amazon, Apple and Kobo.

If you want to convert your files to the EPUB format, several options are available. Please contact us for more information on the conversion programs offered by our partners.

How to troubleshoot your files

SourceURL:file://localhost/Users/patrice/Downloads/fwddeuxfichierstraduits(1)/pour%20traduction_ENG.docIf you have carefully followed our recommendations to create your file, but still get errors when trying to import it and don't understand what they mean, please read the following additional information before contacting us for support.

First, you have to appreciate that it is very difficult for us to diagnose what's wrong with one particular file. Doing so requires an analysis process, and the best people to undertake that are those who created your ePub files.

Different avenues are worth exploring.

If your provider created the ePub file manually, he will probably be able to understand the errors that occurred and may know how to debug the file to make sure it complies with the requirements.

If your provider uses an external tool to generate ePub files (such as InDesign or Pages), he could search for keywords contained in the error message in:

  • the software's documentation
  • the software's user forums
  • online search engines.

If the research isn't fruitful, the next step is to seek advice from a person who knows how to create ePub files from scratch. Such a person will be better able to understand what's wrong with the file and then debug it.

Even if you manage to debug one file, your problem won't be solved at the source, and you will almost certainly encounter similar problems again when you create another ePub file. The best way to prevent this is to find out exactly what causes the error when creating the file, and consequently to change the file creation process to make sure the next files you compile comply with the requirements.