How to test an ebook before you publish

Ebook defects have a habit of appearing after publication, because that is the first time the book meets a reading system you did not test on. The purpose of a testing pass is to compress that meeting into the hour before upload, on the file you will actually send.

The phrase carries the weight: the file you will actually send. An export in an editor’s preview window and the EPUB on disk are different artefacts — the preview reads the program’s state, the upload reads the file — and a defect that exists only in the file is the one that ships. Test the artefact, not the intention.

Layer one: validate

Run epubcheck, the reference validator maintained for the W3C, on the finished file. Every major retailer runs it (or its equivalent) before accepting an upload, so a file that passes locally is unlikely to be rejected on structure.

What it catches: broken markup, missing manifest entries, bad links, invalid metadata — the mechanical failures, error by error, in why your EPUB was rejected. What it cannot catch: anything about how the book reads. That is the next two layers.

Layer two: convert like the retailer will

Open the EPUB in Kindle Previewer — free, for desktop. It runs Amazon’s own conversion and displays the result across simulated devices: e-reader, tablet, phone.

Why this matters more than any simulator: KDP does not display your EPUB. It converts your EPUB into Kindle’s format, and the book readers buy is the conversion’s output. Previewer runs that same conversion locally, so what it shows is what Amazon will sell. A title that renders oddly in Previewer renders oddly on sale — and none of the other reading apps can tell you that.

Use it to check:

• the converted book’s title page, contents, and chapter starts;
• how the reader’s own font settings interact with the book — body text should follow the reader; headings, epigraphs and captions keep the book’s styling;
• images and captions at each device size;
• footnotes and endnotes — links, pop-ups, jumps back.

Layer three: read it

Open the same file in at least one non-Kindle reading app — Apple Books, Calibre’s viewer, Kobo’s — because reading systems differ more than any two web browsers, and the file that is perfect on one can drop something on another.

Then read, actively, with a checklist:

• The contents is complete and every entry lands on the right page.
• Every chapter starts where it should — no chapter beginning at the bottom of a screen.
• The first pages survive the sample. Retailers show the opening ten per cent; that is the storefront, and it deserves a full read.
• Images appear, at sensible sizes, with their captions attached.
• Notes link out and back, on at least one device.
• The metadata is right: title, author, series. This is what the retailer’s catalogue carries, and a wrong author name in the file is a support ticket after launch.
• The cover is the cover you chose — the file’s cover and the listing’s image are set separately on most platforms, and both get checked.

Layer four: a real device, briefly

If you own one, send the file to a real Kindle — Send to Kindle takes EPUB now — or sideload to a Kobo. Ten minutes of reading on the actual hardware catches the residue: fonts the device substitutes, pages that render slowly, and above all the reading experience at true size, which is the thing no simulation reports honestly.

This is the same discipline that catches typographic defects in print: a page proof is looked at as a page, not as a plan. The digital equivalent is reading the converted book on the glass it will actually be read on.

The order that works

1. epubcheck on the file from disk — mechanical validity.
2. Kindle Previewer — Amazon’s conversion, on simulated devices.
3. A second reading app — a different renderer, same file.
4. Read the first ten per cent in full, checklist in hand.
5. A real device, if one is available.

An hour, all told, for the class of defect that otherwise arrives as a one-star review describing exactly what you could have seen on Tuesday.

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Testing is where the “verify it with your eyes” habit matters most in publishing: every layer above has caught, at some point, a book that passed every automated check and was visibly wrong on the page. The machines confirm the structure. Only reading confirms the book.

Nueel exports the EPUB as a file you can run through every layer above — the same artefact the upload would carry — rather than asking you to trust a preview, and its own checks cover the KDP profile’s requirements before the file is even written.

Common questions

How do I test an EPUB before publishing?

Three layers. Validate the file with epubcheck, the reference validator the retailers themselves run. Open it in Kindle Previewer, which runs Amazon's own conversion and shows the book on simulated devices. Then read it — in a reading app and ideally on a real device — checking the TOC links, the chapter starts, the images and the notes.

What is Kindle Previewer?

Amazon's free desktop application. It takes your EPUB and runs the same conversion KDP performs at upload, then shows the result as it would appear on an e-reader, a tablet and a phone. A defect it shows you is a defect Amazon's converter produces, which makes it the closest thing to testing on the storefront before the storefront exists.

Why did my book pass validation but still look wrong?

Because a validator checks structure, not appearance. epubcheck confirms the file is legal EPUB; it cannot tell you that your chapter titles are too small on a phone, or that your image captions collide with the text at a large type size. Only reading the book catches the second class of problem.

Should I test on a real Kindle?

If you can. Send the file to your own Kindle with Send to Kindle, or load it by USB, and read a few chapters. Simulators cover layout; a real device adds the things that only show up there — font substitution on the device's own typefaces, slow pages, and the reading experience at actual size in actual light.