Free · Private · In your browser
EPUB Validator
Find out why KDP, Apple Books or Send to Kindle rejected your book, without uploading your manuscript.
Files never uploaded Works offline Free, no signup No file size limits
How it works
- Drop your EPUB and get a full structural report in seconds.
- Every problem is explained in plain English – what it is, why stores care, how to fix it.
- Follow the “fix this for me” links into the fixer and metadata editor, then re-validate.
Why “no upload” matters
Every conventional converter site works the same way: your file travels to their server, sits in their queue, gets converted on their hardware, and – you hope – gets deleted afterwards. You can’t verify any of it. The FBI has even warned about free converter sites that use that upload as a way to deliver malware or harvest the documents themselves. Your books are yours; a format change shouldn’t require handing them to a stranger.
ebook.tools removes the question entirely. The converter is delivered to your browser as code and runs on your machine; the file you drop is opened from memory, transformed, and saved back – the network isn’t involved at all. That isn’t a policy promise, it’s an architecture, and you can test it: load this page, switch off your wifi, and convert. It works exactly the same, because there was never anything to send.
What the validator checks, and why stores reject books
When KDP says "there's a problem with your file" or Send to Kindle silently swallows an upload, the actual cause is nearly always one of a short list of structural sins – and the store's error message rarely tells you which. This validator opens your EPUB the way a strict reading system does and reports everything it finds, ranked worst-first, in sentences a human can act on.
The checks mirror the rejections that actually happen. Container problems: a missing or malformed mimetype entry, broken container.xml, a package document that isn't valid XML – the classic "file appears corrupt" causes. Manifest and spine integrity: files listed but missing from the archive, spine entries pointing nowhere, duplicate declarations – the causes of blank pages and missing chapters. Broken internal references: images and cross-reference links that point at files which don't exist. Metadata stores insist on: a title, a valid language tag (the single most common silent Send to Kindle rejection), and a proper identifier. And well-formedness of every content file, because one unclosed tag in chapter 12 can fail an entire KDP submission.
Honesty about scope: this is not epubcheck, the Java-based official validator – that tool checks hundreds of specification fine points and runs on servers. This validator is an independent, browser-native implementation focused on the errors that get real books rejected by real stores, and unlike an upload-based epubcheck site, your manuscript never leaves your machine – which matters rather a lot when the book you're validating is unpublished.
Most errors it finds come with a one-click path into the Kindle EPUB fixer or the metadata editor. Fix, re-drop, and submit with confidence.