Frequently Asked Questions
Is Epublys really free?
Yes. All core tools are free with no sign-up required. We also offer a Pro plan for power users who want expanded limits, but the free tier will always exist.
What are the file size limits?
Free tier: 10MB per file (20MB for PDF to EPUB), up to 10 files for merge operations. Pro plan: 100MB per file, up to 500 files. See pricing.
Are my files stored on your servers?
No. Files are processed entirely in memory and are never written to disk or any persistent storage. There is no file to delete because nothing is saved.
What EPUB versions are supported?
Epublys supports both EPUB 2 and EPUB 3 files. The validator checks compatibility with both standards.
Can I convert between EPUB and PDF?
Yes. Our EPUB to PDF converter generates clean PDFs with no watermarks. We also offer a PDF to EPUB converter that extracts text from PDFs and creates reflowable EPUB ebooks — ideal for reading on Kindle, Kobo, or mobile devices.
Does merging preserve formatting?
Yes. The merge tool preserves each book's CSS, images, and chapter structure. It generates a combined table of contents and optional divider pages between books.
Can I use Epublys on mobile?
Yes. Epublys works in any modern browser — desktop, tablet, or phone. No app installation required.
Is there an API?
Yes. Epublys has a REST API and an MCP server for AI agents. Generate API keys from your account page. Full docs at /openapi.json.
What happens if processing fails?
You'll see a specific error message. Common causes: corrupted EPUB files, files that exceed size limits, or unsupported EPUB structures. Try validating your EPUB first to check for issues.
How is this different from Calibre?
Calibre is a full desktop ebook manager (great for large libraries). Epublys is a quick online tool for one-off tasks — no install, no learning curve. Read our full comparison.