Free DOCX preflight
Private EPUB validator online
EPUB validator online for the file you plan to publish.
Inspect the package structure, required metadata, navigation, and spine without sending your book to a remote validator.
✓No manuscript upload✓Package and metadata checks✓Navigation and reading-order checks
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.
What this EPUB preflight checks
An EPUB is a connected publication package, not a single HTML file. A missing container, broken package path, incomplete metadata, or empty spine can prevent a reading system from opening the book correctly.
- application/epub+zip mimetype
- META-INF container path
- Title, language, and identifier metadata
- Navigation document and spine entries
Validation is necessary, but it is not visual proofing
A structurally valid EPUB can still have poor chapter breaks, clipped images, weak accessibility, or inconsistent styling. Test the final file in more than one reading app and inspect its table of contents before release.
FAQ
Frequently asked questions
Is the EPUB uploaded?
No. This free validator opens the EPUB archive locally in your browser.
What does EPUB spine mean?
The spine is the ordered list of content documents a reading system follows through the book. It is unrelated to a printed book spine.
Will this replace EPUBCheck?
No. It is a fast first-pass package check. Use a standards-complete validator and device proofing before a high-risk release.
Found an EPUB problem?
Keep the repaired export, print file, cover, metadata, and launch materials attached to one approved source.