Validate
EPUB Validator
Upload an EPUB to check its structure against the EPUB specification. The validator checks the mimetype, META-INF/container.xml, OPF package file, manifest, spine, table of contents, cover image, and all referenced files. It reports errors, warnings, and suggestions so you can fix issues before publishing.
Input formats
Output formats
Common uses
- Check an EPUB before uploading to Kindle, Apple Books, or Kobo
- Diagnose EPUB errors reported by reading apps
- Verify an EPUB created from a Word document or Markdown
- Check a client's EPUB before editing or formatting
Limitations
- This is a structural validator, not a full epubcheck replacement. For publishing, use the official epubcheck tool.
- DRM-protected files may show false errors because encrypted content cannot be read.
- CSS validation and advanced accessibility checks are not included.
Your e-book files, handled privately
This tool runs entirely in your browser. Your files are never uploaded to a server. This tool does not remove DRM or bypass copyright protection. Only upload files you own or have permission to process.
Frequently asked questions
epubcheck is the official open-source EPUB validation tool from the W3C. This tool performs a subset of the same checks in your browser without requiring a Java installation.
Some reading apps have requirements beyond the EPUB specification, such as specific cover image sizes, font embedding restrictions, or chapter structure expectations. Use the Kindle EPUB Checker or Apple Books Checker for platform-specific issues.
Every EPUB must contain a file named 'mimetype' as the first file in the ZIP, containing the text 'application/epub+zip'. This file identifies the archive as an EPUB to reading apps.