Checking an ebook before you publish it
The print proof has a ceremony around it. You order it, you wait for it, it arrives in a box, and you sit down with a pen. Nobody has to be told to do it.
The ebook has none of that. It is a file that appears in a folder, and the only thing standing between it and a store is you deciding it looks fine. So most authors never check it at all, and the first person to read the book on an actual device is a paying reader.
Replace the ritual with a procedure. It takes under an hour.
Validate the file first
Before you look at anything, run the file through a structural check. An EPUB is a small website in a zip container, and a validator reads it the way a reading app does: broken internal links, files referenced but missing, a malformed contents document, a cover the package never declares, markup that some apps will render and others will silently drop.
None of that is visible by looking. You can read a book front to back and never notice that a chapter is missing from the spine, or that the language is undeclared and every e-reader is guessing at hyphenation.
The target is zero errors and zero warnings. Not "only warnings" — warnings are where the app-specific failures live. What makes an EPUB pass validation covers the common faults and what causes them, so this guide will not repeat it.
Validation is a floor, not a verdict. A file can be perfectly valid and still open on a copyright page in 8 pt type.
Then read it on two real things
A desktop previewer shows you the file the way the program that built it thinks it should look. That is the one opinion you already have.
Load the book onto at least two devices that are not that. A phone is compulsory, because it is where most ebook reading actually happens and it is the smallest thing your layout has to survive. Add either an e-ink reader or a tablet.
They differ in three ways that matter. Size: a phone gives you roughly a paperback column at a third of the width. Contrast: e-ink is reflective and gray-on-gray, so a pale tint that separated a pull quote on a laptop separates from nothing on a reader. Images: apps scale, dither and constrain pictures differently, and a full-width figure that fits on a tablet can push a phone into sideways scrolling.
Send yourself the file and open it. Then read — not skim — the first chapter and one chapter from the middle.
In the Interior Formatter. It builds an EPUB 3 alongside the print PDF from the same manuscript, with a declared language, accessibility metadata, ARIA roles and chapter numbering, generates the contents from the real chapter structure, and carries your image alt text through. It validates with zero errors and zero warnings under epubcheck before you ever send it to a store. Start a book → · about the Interior Formatter
The checklist
With the file open on a device, work down this list.
- The cover appears, and it is sharp. In the library grid and on the first screen. Fuzzy edges or visible blocking means the image went in too small. The size to build to is 1600 × 2560 — see Ebook cover size, and why it is not your print front.
- The contents match the real chapters. Same titles, same order, nothing missing off the end, no stray heading that was never a chapter. Then tap every entry and confirm it lands on that chapter and not the one after it.
- Chapter openings look deliberate. Consistent space above the title, consistent treatment of the number, and a first paragraph that is styled the same way in every chapter.
- The book opens where it should. Ask what page a reader lands on when they first open the file. It should be the start of the story or the first real chapter, not the title page and certainly not the copyright page.
- Italics survived, and so did the special characters. Emphasis, em dashes, ellipses, curly quotes, accents, any symbol you used. See Accents, symbols and characters that go missing.
- Images are visible at a sensible size and are not enormous. A figure should be readable without pinching, and the whole file should not be tens of megabytes because three photographs went in at camera resolution.
- Notes navigate both ways. Tap a reference, land on the note, and find your way back. A note you cannot return from is worse than no note.
- The back matter's links work. Your website, your newsletter, the next book. Tap each one on the device, because a typo in a URL is invisible on screen and fatal at the end of the book.
- The metadata inside the file matches the listing. Title, author and language, exactly as they appear on the store page.
What only shows on a device
Three faults are effectively invisible until the book is on a screen you did not build it on.
Type at the wrong default size. Readers can change it, and most never do. If your body text arrives noticeably larger or smaller than every other book on that device, something in the file is fixing a size that should have been left to the reader.
Images that overflow. A picture sized to a page can force horizontal scrolling on a phone, which no reader will forgive and few will report.
A book that starts on the copyright page. The single most common ebook fault, and the one that costs you the sample. The first screen is the sample, and the sample is the sale.
Make yours
Everything here is built into the tools, and they are free to use: name your book, bring your manuscript or your artwork, and work as long as you like. You only pay when you want the files without the preview watermark.
Next: Check the listing the way a stranger would · More: What makes an EPUB pass validation · Links in an ebook, and where they should point · The proof checklist, front to back