EPUBCheck-TS

Free Online EPUB Validator

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About This Online Validator

This is a free online EPUB validator that checks your ebook files for errors and compatibility issues. Whether you're an author, publisher, or designer, this tool helps ensure your EPUB files meet the official EPUB specification before publishing. It's powered by EPUBCheck-TS, an open-source JavaScript library.

100% Private - Your Files Stay on Your Computer

Unlike other online validators, your EPUB file is never uploaded to any server. All validation happens entirely in your web browser using WebAssembly technology. Your manuscript, your content, your data - it all stays on your computer. Nothing is transmitted over the internet.

Fast and Instant Results

Get validation results in seconds. No waiting for server processing or queue times. The validator runs locally on your device, so it's as fast as your computer allows.

What Does It Check?

Structure - Verifies the EPUB container format and required files
Metadata - Checks title, author, language, and other book information
Content - Validates XHTML, CSS, and navigation documents
Accessibility - Detects missing alt text, empty links, and other a11y issues
Cross-references - Ensures all internal links and resources are valid

Supported EPUB Versions

This validator supports EPUB 2.0, EPUB 3.0, 3.1, 3.2, and 3.3. It automatically detects the version of your ebook and applies the appropriate validation rules.

Current Limitations

This tool catches most common EPUB errors but doesn't cover everything yet. It currently detects about 70% of the issues that the official EPUBCheck tool would find. For final publishing, we recommend also checking with the official tool if you need comprehensive validation. We're actively improving coverage.

Who Is This For?

Authors - Check your ebook before publishing on 3ook.com, Amazon, Apple Books, or Kobo
Publishers - Quality assurance for your publishing workflow
Designers - Validate ebook layouts and styling

For Developers: EPUBCheck-TS Library

This online validator is powered by EPUBCheck-TS, an open-source EPUB validation library for JavaScript and TypeScript. If you're a developer looking to integrate EPUB validation into your own applications, you can use the same library directly.

Why a JavaScript EPUB Validator?

The official EPUBCheck tool is written in Java, which makes it difficult to integrate into JavaScript/TypeScript projects or run directly in web browsers. EPUBCheck-TS solves this by providing a native JavaScript EPUB validator that you can import like any other npm package. No Java runtime required, no command-line wrappers, no server-side processing needed.

Install via npm

npm install @likecoin/epubcheck-ts

Key Features

TypeScript-first - Full type definitions included, great IDE support and autocompletion
Browser & Node.js - Works in any JavaScript environment, no native dependencies required
WebAssembly-powered - Uses libxml2-wasm for fast, accurate XML/RelaxNG/XSD validation
Zero native deps - Pure JavaScript/WASM, no compilation needed, works on any platform
Same message IDs - Compatible error codes with official EPUBCheck (PKG-*, OPF-*, CSS-*, HTM-*, etc.)

Use Cases

EPUB generation tools - Validate EPUBs created by your application before delivery
Publishing platforms - Check uploaded ebooks for errors on the server or client-side
CI/CD pipelines - Automate EPUB quality checks in your build process
Electron apps - Build desktop EPUB editors with built-in validation
Browser extensions - Create tools that validate EPUBs without server round-trips

Open Source

EPUBCheck-TS is open source and available on GitHub. Contributions are welcome! Check out the npm package for installation instructions, or browse the API documentation.

Validation Results