Apple Books takes EPUB only, requires EPUB 3, and every file must pass EPUBCheck before it is accepted. Kobo Writing Life takes .doc, .docx, .odt, .epub or .mobi up to 100MB and converts whatever you give it, running its own validation afterwards. Apple is the strictest major retailer. Kobo is the most forgiving.
Neither accepts PDF.
Apple Books
EPUB version. The Apple Books Asset Guide states that "Apple Books supports the EPUB 3.3 specification, and is backwards compatible with previous versions of EPUB 3", and that the current Asset Guide covers EPUB 3 files only. EPUB 2 is no longer documented. Chinese and Japanese titles are listed with a minimum EPUB version of 3.
Validation is a hard gate. Apple states plainly that "All books submitted to Apple Books must pass the latest version of EPUBCheck". Apple never pins a version number, saying only "the latest". At the time of writing that is EPUBCheck 5.3.0, which validates against EPUB 3.3.
Apple then runs its own checks on top. Books must pass Transporter validation, all files inside the EPUB must be listed in the package manifest or the book fails import, and only UTF-8 and UTF-16 encodings are permitted. Unmanifested files are one of the common validation errors, so a file that fails EPUBCheck will usually fail Apple twice over.
Cover. RGB colour, at least 1400 pixels along the shorter axis, as a high quality JPEG or PNG. Apple explicitly rejects upscaled images: do not enlarge a smaller file to reach the minimum, because "excessively blurry or pixelated images are rejected".
Size limits. No single image inside the EPUB may exceed 5.6 million pixels, and the book itself is capped at 2GB by the ZIP standard.
DRM is applied by default. Text, fonts and images are encrypted unless you opt out, while audio, video and embedded PDFs are not. If you want a DRM free title you have to say so.
You do not need a Mac. Individual authors publish through Apple's web portal, which needs no particular operating system. Bulk deliveries use Transporter, Apple's command line tool, which officially supports macOS, Windows 11 and Red Hat Enterprise Linux. Two related pieces of folklore are also out of date: the tool is Transporter rather than iTunes Producer, which no current documentation mentions, and the account portal is called iTunes Connect rather than Books Connect, which is not a product name Apple uses.
Kobo Writing Life
Accepted formats. ".doc and .docx, .odt, .ePub, .mobi", all converted into a Kobo formatted EPUB. PDF appears in no accepted format list.
File size. 100MB, whatever the format.
EPUB version. Kobo does not state one. Its documentation never specifies EPUB 2 or EPUB 3 anywhere. Anyone quoting you a version for Kobo is not getting it from Kobo. Supplying EPUB 3 is the sensible default, since it is the only version still maintained.
Validation is required but the gate is softer. Every book is run through EPUB validation whatever format it arrived in. Critical errors must be fixed before publishing. Non critical errors do not block publication on Kobo itself, but they do block distribution to OverDrive, so a file with warnings can sell on Kobo and quietly fail to reach libraries. Kobo does not name EPUBCheck, saying "You can use any ePub validator" and recommending the free pagina validator.
What conversion loses. If you upload a Word file, Kobo warns that "the Word doc is not a good indicator of what the ePub file will look like" and that margins and spacing can differ substantially. Named losses: headers and footers are unsupported, columns are unsupported, and endnotes are supported while footnotes are not. If your book uses footnotes, convert them to endnotes before uploading a Word file, or supply a finished EPUB instead.
Cover. Under 5MB, JPG or JPEG preferred with PNG acceptable, 300 DPI recommended but 72 DPI accepted. Kobo asks for a 3:4 width to height ratio to match its device screens. It states no absolute pixel dimensions and says nothing about colour space.
Which Is Stricter, and What That Means for You
Build to Apple's requirements and you will clear Kobo automatically. The reverse is not true: a file that Kobo happily converts and sells can fail Apple's import outright.
The practical approach is to make one EPUB 3 file that passes EPUBCheck cleanly, supply that to both, and let Kobo's converter do nothing. Uploading a Word file to Kobo is a convenience that costs you control over the result and silently drops footnotes.
For what the format requires generally, see how to make an EPUB file, and for Amazon's separate rules, Amazon KDP EPUB requirements.
What Deckle Exports
Deckle exports EPUB 3, which is what Apple supports and what IngramSpark names explicitly.
Worth clearing up a point of confusion here, because the package document declares version="3.0" and that looks like an old version number. It is not. The EPUB 3.3 specification requires that attribute to "have the value 3.0 to indicate conformance with EPUB 3", and explains why in a note: "Updates to this specification do not represent new versions of EPUB 3 (i.e., each new 3.X specification is a continuation of the EPUB 3 format)." Every EPUB 3 file declares 3.0, including a current EPUB 3.3 one. There is no way to declare 3.3 there, and no retailer expects one.
The container is built directly rather than zipped from a folder, so the mimetype rules that cause most validation failures are handled by construction. All four metadata items EPUB requires are written, including the dcterms:modified timestamp in the exact form the specification demands. The output is reflowable, which is what a novel should be.
One thing to check before uploading to Apple. The navigation document is only written when the Include table of contents option is on. That document is required by the EPUB specification, so an export with the option off will fail EPUBCheck, and Apple rejects anything that fails EPUBCheck. Leave the option on for EPUB export even if you do not want a visible contents page. Why a novel still needs one is covered in do novels have a table of contents.
Footnotes and Kobo. Deckle can produce either footnotes or endnotes. If you are uploading a Word file to Kobo rather than an EPUB, switch to endnotes first, because Kobo's converter does not support footnotes. Supplying the EPUB directly avoids the problem entirely.
Deckle does not produce cover images. Apple's 1400 pixel RGB minimum and Kobo's 3:4 ratio are both jobs for a cover designer.
Common Mistakes
- Uploading a PDF. Neither platform accepts one.
- Exporting an EPUB without the table of contents option. The navigation document is required, and Apple gates on EPUBCheck.
- Assuming Kobo's silence means EPUB 2 is fine. It states nothing. Use EPUB 3.
- Ignoring Kobo's non critical errors. They do not block Kobo, but they do block OverDrive.
- Uploading Word to Kobo with footnotes in it. They are dropped. Endnotes survive.
- Upscaling a small cover to reach Apple's 1400 pixel minimum. Apple rejects blurry and pixelated images.
- Believing you need a Mac for Apple Books. Transporter runs on Windows and Linux, and the web portal runs anywhere.
FAQ
Q: Does Apple accept EPUB 2? A: It is no longer documented. Supply EPUB 3.
Q: Which EPUBCheck version does Apple run? A: Apple says only "the latest". It does not publish a version number.
Q: Can I upload a Word file to Apple Books? A: No. Apple takes EPUB, or Multi-Touch books made in Apple's own tools.
Q: Does Kobo add DRM? A: It is per title and opt in, delivered as Adobe DRM.
Q: What size should my cover be? A: For Apple, at least 1400 pixels on the shorter side, in RGB. For Kobo, a 3:4 ratio under 5MB. A single file meeting Apple's minimum at 3:4 satisfies both.