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EPUB Validator & Checker
Free online EPUB checker and validator — no signup. Catch the structural, well-formedness, and reference errors that get books rejected from KDP and Apple Books.
Select EPUB files
or drop EPUBs here
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Frequently asked questions
- What does the EPUB validator and checker look for?
- It checks the structural and content classes that get books rejected from stores: ZIP integrity, the mimetype and META-INF/container.xml, the OPF package (a missing dc:identifier is an error; a missing title or language is flagged), duplicate manifest IDs, broken manifest hrefs, spine entries pointing at missing items, and an EPUB 3 nav document. The default deep scan also reports XHTML that isn't well-formed, broken internal links, missing images, images without alt text, and pages missing a lang attribute. You get a plain error/warning list, not a pass-fail black box.
- Is this an online version of EPUBCheck?
- No — it is a separate, browser-based checker, not EPUBCheck and not a full reimplementation of it. It overlaps EPUBCheck on the structural, well-formedness, and reference error classes above — the ones that most often cause KDP, Apple Books, and Kobo to reject an upload — so it's a fast first pass with no Java install. It does not run the full EPUBCheck schema/RNG suite, validate CSS, fetch remote resources, or check media overlays. For a guaranteed-complete store submission, run the official EPUBCheck as your final gate.
- Does it fix the errors it finds, or only report them?
- Both, but auto-fix is deliberately narrow. It repairs exactly three safe things: it writes the correct mimetype (creating it, stored uncompressed, if missing), regenerates a missing META-INF/container.xml, and injects a missing dc:language as 'en'. Everything else — duplicate IDs, manifest/spine mismatches, broken links, malformed XHTML, a missing title or identifier — is reported for you to fix by hand, because auto-rewriting those risks corrupting your book.
- Can it check both EPUB 2 and EPUB 3?
- Yes. It detects the version from the OPF and applies the right checks — for example, the EPUB 3 nav-document requirement only triggers on EPUB 3 files.
- Does running the checker change or upload my file?
- Checking is read-only and never modifies your EPUB. Auto-fix produces a new downloadable file and leaves your original untouched. Files are processed over HTTPS in memory only — never written to disk or persistent storage — and discarded the moment the response returns.