Private EPUB validator online
EPUB error reference
Turn EPUB error codes into a file, cause, and repair step.
Do not fix only the wording of an error. Identify the package layer—container, OPF metadata, navigation, XHTML, CSS, media, or accessibility—then validate the replacement file again.
✓Package-layer diagnosis✓Private first-pass check✓Official validator linked
Private by default
Drop in the file you plan to publish
Choose a DOCX or EPUB. This first check runs in your browser; your manuscript is not uploaded.
Read the location before the message
A validator result usually identifies a severity, code, file path, line, and explanation. The path tells you whether the failure lives in package.opf, nav.xhtml, a chapter document, CSS, or a media asset. Repair the source that generates that file whenever possible; hand-editing the export can be overwritten on the next build.
| Layer | Typical problem | Repair direction |
|---|---|---|
| Container | Missing or wrong package path | Repair META-INF/container.xml |
| OPF metadata | Missing title, language, identifier | Complete publication metadata |
| Manifest or spine | Missing item or broken reading order | Rebuild references and order |
| XHTML | Invalid nesting or duplicate IDs | Fix semantic document markup |
| Navigation | Broken target or missing nav | Rebuild table of contents links |
| Media | Missing file or wrong media type | Add the asset and correct manifest type |
Use the official validator as the final standards check
ShipMyBook's browser tool is a bounded structural preflight. EPUBCheck is the open, standards-complete reference used across the publishing ecosystem. Run the current release after every repair and proof the book in real reading systems; zero validator errors does not guarantee a good visual or accessible reading experience.
FAQ
Frequently asked questions
Is every warning a release blocker?
No. Severity and platform requirements matter. Understand the warning and document the decision instead of automatically suppressing it.
Why does an EPUB still look wrong after passing validation?
Validation checks standards and structure. CSS, image behavior, font fallback, device differences, and accessibility still require proofing.
Found the package layer? Repair and validate again.
A paid release can keep the repaired EPUB tied to its source, print file, cover, and metadata.