About Epub Studio
A set of ebook tools that run on your device, not on ours — because that is both faster and none of our business.
Epub Studio is 21 tools for working with ebooks: converters in both directions, a reader, and a set of utilities for fixing files that will not open. There is also Style Studio, which re-typesets a book — typeface, spacing, theme, margins — and writes those choices into the file you download.
Everything runs in your browser
Most online converters work by uploading your file, processing it on a server, and letting you download the result. That means your book sits on someone else's machine, and you are trusting a promise about what happens to it there.
This site does the work locally instead. The conversion code is JavaScript that runs on your device, so your file is never transmitted. It is faster for anything of a reasonable size, it works with a bad connection, and it makes the privacy question moot rather than a matter of trust. The privacy page spells out the details.
What that costs
Being honest about the trade-off: two things do not work this way. Writing MOBI and AZW3 requires Amazon's own toolchain, which cannot run in a browser. Rather than make an exception and upload your book, those pages explain what to do instead — which, since Send-to-Kindle started accepting EPUB in 2022, is usually nothing at all.
Very large files are also bounded by your device's memory rather than a server's. A novel is trivial; a 500 MB art book may struggle on an old phone.
Why EPUB
EPUB is an open W3C standard, which means anyone can write software that reads it and no company can withdraw that. A book in EPUB will still open in software nobody has written yet. A book in a proprietary format depends on a company continuing to care.
That is the argument running through most of what is here: keep your library in the open format, generate device-specific copies when you need them, and treat those copies as disposable.
Free, and no account
Every tool, every file size, no sign-up. There is no paid tier and nothing held back. Since the work happens on your device, serving these tools costs about as much as serving a blog.
Built on open source
This site would not exist without a lot of other people's work — among others JSZip for reading and writing the EPUB container, pdf.js for text extraction, Mammoth for Word documents, and jsPDF for typesetting PDFs. The reading typefaces are open-licensed, including Atkinson Hyperlegible and OpenDyslexic.
The blog, and how it is written
The blog covers how ebook formats actually work, how to fix files that readers reject, and how to make a book pleasant to read. It is written to be useful whether or not you use any of these tools.
How it is made, plainly: posts are drafted with AI assistance and edited by the same people who build the tools. When an article describes how a converter behaves, we run the conversion and describe what actually happened rather than what should happen. Outside facts link to their primary sources, and when a post is substantively corrected, its dated timestamp is updated. If something here is wrong, we would rather fix it than rank with it.