What validation catches
Validation can identify structural and packaging problems such as missing resources, incorrect manifests, invalid markup, broken references, and specification violations. Those errors can cause display failures or distribution problems.
Why retailers care
Retailers and distribution platforms expect well-formed files. Kobo, for example, explicitly recommends validating EPUB files and warns that errors can cause display issues or prevent distribution to partner sites.
What EPUBCheck does not prove
A file can be technically valid and still have poor typography, confusing navigation, weak alternative text, unhelpful metadata, or a bad reading order. Validation answers “is this structurally conformant?” rather than “is this a good book experience?”
A better preflight
Use validation together with navigation review, accessibility checks, metadata comparison, and previewing in target reading systems or retailer tools.
Primary sources
- W3C EPUB 3.3 — EPUB conformance requirements
- Kobo EPUB Best Practices — retailer recommendation to validate EPUB files