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EPUB Checker

Validate your EPUB files for structure, metadata, and best practices — instantly, for free.

Free tool

Drag and drop your .epub file here

or

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Max file size: 200 MB · EPUB 2 & EPUB 3

Your file is processed securely and deleted immediately after analysis.

Structure Validation

Checks ZIP integrity, mimetype, container.xml, OPF package document, manifest, and spine reading order.

Content Validation

Validates XHTML well-formedness, UTF-8 encoding, internal references, and duplicate ID detection across content documents.

Best Practice Analysis

Reviews file sizes, image optimization, naming conventions, and cover image declarations.

What the EPUB Checker does

An EPUB is really a small website zipped into a single file — XHTML content, a manifest, navigation and metadata, all bound by the EPUB standard. When any of those pieces is malformed, reading systems and retailers reject the file or render it incorrectly. This free EPUB validator runs your file through epubcheck, the canonical validator behind the EPUB specification, and tells you exactly what to fix.

Upload a file and you get every fatal error, error and warning surfaced with the rule it breaks and where it occurs — from ZIP and mimetype problems to broken internal references and spine reading order. It is the same conformance check that stores like Amazon Kindle, Apple Books, Google Play Books and Kobo run before they accept a title, so passing here means passing there.

The check is free, runs online, and processes one book at a time. Your file is analyzed securely and deleted immediately after.

When to use it

  • Before sending a title to a retailer, aggregator or library — to avoid a rejection.
  • After a conversion or export, to confirm the output is valid EPUB 2 or EPUB 3.
  • When a reader reports a book that will not open or renders strangely.
  • As a quick quality gate on files you receive from authors or partners.
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Validated with epubcheck 5.1.0, the canonical EPUB validator maintained by the W3C and released under the BSD-3-Clause license. EPUB is a registered trademark of the W3C.