Convert any ebook.
Keep it beautiful.
Free EPUB tools that run in your browser. No signup, and your files never leave your device.
Convert from EPUB
3 tools · 2 guidesConvert to EPUB
12 toolsEPUB utilities
7 toolsHow it works
- 01 Drop a file Choose a book from your device, or drag it onto the zone above.
- 02 It converts in your browser The conversion runs on your own machine. Nothing is queued and nothing waits.
- 03 Download the result The finished file saves straight to your downloads folder.
Epub Studio runs its converters as JavaScript inside the page you are already on. Your file is read from disk into the tab’s memory, transformed there, and handed back as a download. No file is transmitted to a server, so there is no upload queue, no processing wait and nothing stored anywhere afterwards.
Why your files never leave your device
Epub Studio converts files inside your browser tab. When you choose a book, the browser’s File API hands the page a reference to it; the conversion code reads the bytes into memory, builds the output there, and gives it back to you as a download. At no point is the file sent anywhere. There is no server that could receive it.
You do not have to take that on trust. Open your browser’s developer tools, switch to the Network tab, and convert something. You will see the page’s own scripts load and then nothing else — no request carrying your book, no upload of any size. A claim you can check in ten seconds is worth more than a policy page.
Practically, that makes Epub Studio safe for work you cannot put on someone else’s machine: unpublished manuscripts, client documents, contracts, internal reports, anything under an NDA. The file’s privacy is a property of how the tools are built, not a promise about how carefully an upload would be handled.
The exceptions, in full: there are none — Epub Studio loads no analytics, no error reporting, no advertising and no cookies, and serves its fonts from this site rather than a CDN, so the only record of a visit is the ordinary page-request log any web host keeps.
Ebook formats compared
Eight formats show up in almost every ebook question. This table sets out what each one is for, whether its text reflows to the screen, and where it opens.
| Format | Best for | Reflowable or fixed | Works on | Notes |
|---|---|---|---|---|
| EPUB | Everyday reading, and keeping a master copy | Reflowable | Kobo, Nook, Apple Books, Google Play Books, phones, tablets; Kindle via Send to Kindle | An open standard published by the W3C. Two versions are in circulation, EPUB 2 and EPUB 3. |
| Printing, and layouts that must not move | Fixed | Every desktop, phone, browser and most e-readers | Pages keep their exact layout, so a small screen means zooming and panning. | |
| AZW3 | Sideloading a file onto a modern Kindle | Reflowable | Kindle hardware and Kindle apps | Amazon’s KF8 format. Epub Studio reads AZW3 but cannot write it in a browser. |
| MOBI | Kindles too old to accept anything newer | Reflowable | Older Kindle hardware and apps | Effectively retired: Send to Kindle stopped accepting MOBI in 2022. |
| DOCX | Writing and editing a manuscript | Reflowable | Word, Google Docs, LibreOffice, Pages | Not an ebook format — no e-reader opens it directly — but it keeps edits and comments. |
| TXT | Plain text with no structure to lose | Reflowable | Everything, including the oldest devices | No images, no styling, no chapter marks. The smallest possible file. |
| FB2 | Books from FictionBook libraries | Reflowable | FictionBook-aware apps such as FBReader and CoolReader | One XML file holding text and metadata together. Rarely supported outside those apps. |
| CBZ | Comics and manga | Fixed (page images) | Comic readers on desktop, phone and tablet | A ZIP of page images in reading order. Converting CBZ to EPUB makes an archive that ordinary ebook apps will open. |
Which format for which device
- Modern Kindle EPUB
- Amazon’s Send to Kindle has accepted EPUB since 2022, so a modern Kindle usually needs no conversion at all. A sideloaded AZW3 file also works, though Epub Studio cannot write that format in a browser — the page on EPUB to AZW3 for Kindle explains why, and what to do instead.
- Older Kindle MOBI
- Kindles that predate Amazon’s 2011 KF8 rebuild read MOBI and nothing newer. Writing MOBI needs Amazon’s own toolchain, which cannot run in a browser, so the page on EPUB to MOBI for older Kindles sets out the routes that work rather than offering a converter that would have to upload the book.
- Kobo, Nook, Apple Books, Google Play Books EPUB
- These readers open EPUB directly, so a book already in that format needs nothing done to it. A course pack or report that arrived as a PDF is the exception: make a PDF reflowable first, and the text will resize to the screen instead of forcing you to zoom.
- Printing, or a layout that must not move PDF
- Anything headed for a printer belongs in PDF, because PDF pages are fixed. Epub Studio can convert EPUB to PDF with real, selectable text and a trim size you choose, rather than photographing each rendered page.
- Editing a manuscript DOCX
- Editing a book means taking it back to a word processor. Epub Studio can open an EPUB in Word, keeping headings, paragraphs and emphasis so the structure survives the round trip into Word, Google Docs or LibreOffice.
Four people this was built for
Indie authors
Most self-published books are written in Word and have to be delivered as EPUB. Epub Studio can turn a manuscript into an ebook, and the heading styles already in the document become the book’s table of contents.
Students and researchers
Course readings and papers arrive as fixed PDFs, which are painful on a phone. Converting one to EPUB lets the text reflow and the type size follow your eyes. Epub Studio can also read EPUB files in your browser without installing anything.
Publishers and KDP uploaders
Store ingestion rejects files for structural reasons that are rarely explained clearly. Before submitting, validate your EPUB to find the missing package file, broken manifest entry or malformed XML behind the rejection.
Comic readers
Comics and manga arrive as CBZ archives, which most ebook apps ignore. Epub Studio can convert CBZ comics into a PDF that opens on any device, with the pages kept in reading order.
Epub Studio, Calibre and server-based converters
Epub Studio is not the right tool for every ebook job. Here is where each of the three common options is genuinely stronger, including the places Epub Studio loses.
Calibre
Calibre does more than Epub Studio does. It manages an entire library, converts between far more formats, edits EPUB internals directly, and pushes books to e-readers over USB. The costs are that it has to be installed, it is a large program, and its conversion settings take real time to learn.
Server-based online converters
Services such as Zamzar, CloudConvert and Online-Convert support formats no browser can produce, because they run full desktop toolchains on their own machines. The trade-off is that your file is uploaded to a company’s server and processed there, and free tiers usually cap file size or the number of conversions per day.
Epub Studio
Epub Studio installs nothing and uploads nothing — the converters run in the tab that is already open. The real limitation is memory: the whole file is held in RAM while it is converted, so a very large illustrated book can fail on an older phone where a desktop program would cope. Writing MOBI and AZW3 is also impossible in a browser.
What Epub Studio is built on
- JSZip 3.10.1
- Reads and writes the EPUB and CBZ ZIP containers.
- pdf.js 6.1.200
- Extracts text and structure when a PDF is the input.
- jsPDF 4.2.1
- Typesets the output PDF as real, selectable text.
- Mammoth 1.12.0
- Converts Word documents into clean HTML.
- docx 9.7.1
- Writes the .docx file when an EPUB is converted to Word.
- @lingo-reader/mobi-parser 0.4.6
- Parses MOBI and AZW3 containers.
- marked 18.0.6
- Parses Markdown input.
Epub Studio reads EPUB 2 and EPUB 3. Every converter that produces an EPUB writes EPUB 3, the current version of the standard.
The validator is Epub Studio’s own structural checker running in your browser — not EPUBCheck, which is a Java program and cannot run in a browser tab. It checks the mimetype entry, container.xml, the package document’s XML and required metadata, that every manifest href resolves to a file in the archive, that the spine is not empty, and that a navigation document exists.
- DRM-protected files are not supported. Epub Studio cannot open them, cannot convert them, and does not remove DRM — here or anywhere. Most Kindle Store purchases and library loans are encrypted and will fail to open in any converter.
- Writing MOBI and AZW3 requires Amazon’s toolchain and is not possible in a browser, so those pages explain the working route instead of offering a converter.
- Very large files are bounded by your device’s memory, because the whole file is held in RAM while it converts.
Questions people ask
Is Epub Studio free?
Yes. Every tool on Epub Studio is free, with no account, no trial and no paid tier. There is no conversion quota and nothing is watermarked. Because the tools run on your own device rather than on a server, serving them costs about as much as serving a plain web page.
Are my files uploaded to a server?
No. Epub Studio converts files inside the browser tab, using JavaScript the page has already loaded. Your file is read from disk into memory, transformed there, and handed back as a download. Open the Network tab in your browser’s developer tools during a conversion: no request carries the file.
Is there a file size limit?
Epub Studio sets no size cap, because nothing is uploaded and no server quota applies. The practical ceiling is your device’s memory, since the whole file is held in RAM while it converts. A novel is trivial on any machine. A very large illustrated book may fail on an older phone.
Can Epub Studio remove DRM?
No. Epub Studio cannot open DRM-protected files, cannot convert them, and does not remove DRM. Most Kindle Store purchases and library loans are encrypted, and no converter can read them. The tools work on DRM-free files: your own exports, sideloaded books and purchases from DRM-free stores.
Does Epub Studio work offline?
Partly. Epub Studio installs no offline cache, so the page itself has to load over the network the first time. Once a tool has loaded, the conversion needs no connection at all, because the work happens on your device. Losing your connection mid-conversion does not interrupt it.
Which EPUB versions does Epub Studio support?
Epub Studio reads both EPUB 2 and EPUB 3. Every converter that produces an EPUB writes EPUB 3, which is the current version of the standard. The validator accepts EPUB 2 files and flags them with a note rather than an error, since most reading apps still open them without trouble.
Do I need to create an account?
No. Epub Studio has no accounts, no sign-in and no email capture. Drop a file, convert it, download the result and close the tab. Nothing is recorded about who you are, beyond the ordinary access log that any web host keeps of which pages were requested.
What formats can Epub Studio convert to and from?
Epub Studio converts EPUB to PDF, DOCX and TXT, and converts PDF, DOCX, TXT, Markdown, HTML, FB2, MOBI, AZW3 and CBZ into EPUB. CBZ, MOBI and AZW3 also convert straight to PDF. Writing MOBI and AZW3 is not offered, because that requires Amazon’s own toolchain.
Will converting to PDF preserve my formatting?
Mostly. An EPUB reflows to any screen while a PDF has fixed pages, so Epub Studio must choose a page size, margins and typeface when rendering one. Headings, paragraphs, images and emphasis carry across. Style Studio lets you set the typography first.
Which format should I use for Kindle?
Send an EPUB. Amazon’s Send to Kindle has accepted EPUB since 2022 and converts it on Amazon’s side, so a modern Kindle needs no local conversion. AZW3 suits sideloading a file directly onto modern Kindle hardware. MOBI is only for Kindles too old to accept anything newer.
Why is my EPUB file so large?
Images, almost always. Cover art and interior illustrations saved at print resolution dominate an EPUB’s size, while the text itself is rarely more than a megabyte. Recompressing those images is the fix, and it is possible to reduce EPUB file size without touching the text.
Why will my EPUB not open on my e-reader?
Usually something structural: a missing package document, a manifest entry pointing at a file that is not in the archive, malformed XML, or an empty spine. Epub Studio’s validator checks each of those in the browser and names the specific failure instead of reporting a generic error.
Latest from the blog
Epub Studio publishes guides on how ebook formats actually work, how to repair files that readers reject, and how to make a book pleasant to read. The three most recent posts are below, and the blog holds the rest.
Last updated — the date this page was last built.