How to Validate Ebooks – From Code to Reader Experience
Written by
Monika Zarczuk-Engelsma
Elena Bugrova
Posted on
Dec 8, 2025
Category
Accessibility
Once an eBook is ready, it may seem that the work is done. In reality, it's just the beginning of the most important stage – validation, which involves testing the quality and accessibility of the file. At Have a Book, this process takes up to half the production time. Why? Because a technically accurate and accessible e-book isn't just a matter of standards—it's a guarantee of comfortable reading and equal access to content for all readers.
Three Stages of Ebook Validation
The process of ebook validation (usually in EPUB 3 format) is divided into three stages:
Automated testing – detection of technical errors and non-compliance with standards.
Manual testing – assessing the correctness of the file structure and its appearance in various environments.
Testing with screen reader users – checking the real accessibility of the publication for blind individuals.
Each of these stages plays a different role and together they create a coherent quality assurance process.
1. Automated testing – the technical foundations of quality
First, an ebook undergoes a technical review to detect errors in its code and structure. The most commonly used tools include:
EPUB-Checker – an application developed by Pagina, used to validate a file's compliance with the EPUB 2.0 and EPUB 3.0 formats. It indicates errors in the structure, missing files, and incorrect code references.
Ace by DAISY – an advanced ebook accessibility testing tool. It analyzes document semantics, identifying errors related to navigation, headings, alternative image descriptions, and table of contents structure.
The results from these tools allow you to identify the most common issues, such as:
no logical hierarchy of headings,
incorrectly rooted or unlabeled images,
internal links not working properly
errors in the HTML structure or manifest file (OPF).
This is a necessary, but not sufficient, step – because correct code does not always mean correct operation in practice.
2. Manual testing – does the file work the as it should?
The next step is manual testing, which allows us to verify how the ebook behaves in various eReaders and applications. At Have a Book, we test files in Apple Books and Thorium Reader, among others. Each of these devices interprets the EPUB code slightly differently, so the publication may appear differently depending on the environment.
During manual testing, we evaluate, among other things:
metadata consistency (title, author, language, identifier),
heading structure and logical hierarchy
operation of the table of contents and navigation links,
visual consistency with the original (layout, tables, colors),
operation of interactive elements (links, indexes, footnotes),
correct display on various devices and screen resolutions.
Manual validation is also the time to verify details that no automated system can spot – for example, whether footnotes are legible, whether tables are not spread out in the small windows of the reader, or whether the table of contents actually leads to the correct chapters.
3. Accessibility testing – or ebook as seen (and heard) by the user
For a complete quality assessment, it's not enough that an e-book opens correctly—it must also be accessible for people with visual impairments. Therefore, the final stage of validation involves testing with screen reader users.
As Paweł Miąsik, a blind tester working with Have a Book, points out, testing ebook accessibility is similar to auditing a website – except that a book has its own structure, requiring a different approach. The key elements are:
correct hierarchy of headings (chapters, subchapters),
logical and accessible table of contents navigation,
proper functioning of footnotes (the ability to easily switch between them and the text),
clear, described tables,
alternative texts for graphics,
functioning internal and external links,
correct pagination and content search.
Screen readers such as NVDA (Windows), JAWS, VoiceOver (macOS, iOS), and TalkBack (Android) are most commonly used in tests, combined with speech synthesizers such as Espeak or RHVoice.
Thorium Reader, thanks to its open source code and high EPUB 3 compatibility, allows simulating the behaviour of a screen reader directly accessible to users.
Collaboration Is the Key to Success
The best results come from collaboration between the technical team and the accessibility tester. At Have a Book, the validation process is a dialogue: the tester identifies issues, the team makes corrections to the code, and then the file is retested. This allows for the refinement of details that might not be detected automatically.
As Paweł Miąsik points out, a model that could be called ideal could resemble the beta testing process known from software development – the ebook would first be distributed to a test group of recipients who would submit comments, and then the file would be revised and released in its final version. This approach helps avoid recurring errors and continuously improve the quality of the publication.
Why Validation Pays Off
A well-validated ebook means:
fewer complaints and technical problems after its publication,
better compliance with legal requirements (e.g. European Accessibility Act – EAA),
positive user experience,
better visibility in shops and digital libraries supporting accessibility.
Moreover, validation isn't just about checking—it's part of the learning process. Every error detected and every correction increases the publishing team's experience and brings subsequent publications closer to full compliance with standards.
For the curious: recommended sources and tools
Ace by DAISY – https://daisy.org/activities/software/ace/
EPUB Checker – https://pagina.gmbh/epub-checker
Thorium Reader – https://www.edrlab.org/software/thorium-reader/
NVDA Screen Reader – https://www.nvaccess.org/
QA for Accessible Ebooks – https://laurabrady.ca/blog/qa-for-accessible-ebooks
Useful sources:
https://op.europa.eu/en/web/accessibility/transcript-testing-accessible-epubs?utm_source=chatgpt.com
https://accessibility.umich.edu/how-to/documents/test-epub-files?utm_source=chatgpt.com
https://kb.daisy.org/publishing/docs/epub/validation/overview.html?utm_source=chatgpt.com
https://www.accessiblepublishing.ca/evaluating-your-epubs-accessibility/?utm_source=chatgpt.com