How ebook.tools works
“Your files never leave your device” is an easy thing to claim and a hard thing to prove. This page is the proof.
The plain-English version
When you visit a tool page here, your browser downloads two things: the page itself, and a small conversion program written in JavaScript and WebAssembly – the same technologies that run web games and Google Docs. When you drop a file, that program opens it on your computer, rebuilds it in the new format on your computer, and hands the result straight back to your Downloads folder. At no point does the file travel anywhere. There is no “uploading… 47%” bar on this site because there is nothing to upload.
This is the same trust model as a desktop app like Calibre – the software comes to your machine, not the other way around – without the install, and with the browser’s sandbox wrapped around it for good measure.
The airplane-mode test
Try this right now. Open any converter page, then switch on airplane mode (or just turn off your wifi). Drop a file. It converts exactly as before – because the conversion never needed the internet in the first place. No upload-based site on earth can pass this test.
The technical version
Each tool page loads only the code for its own conversion: a reader that parses the
input format into a neutral in-memory book model, and a writer that serializes that
model into the output format. The heavy work runs in a Web Worker, so the page stays
responsive while a big book converts. Format parsing builds on the open-source
foliate-js reader library, zip
handling on fflate, RAR extraction on a
WebAssembly build of libarchive, and PDF assembly on
pdf-lib. Our conversion engine –
@ebook-tools/core – is open source, so “the code runs locally” is a checkable
statement, not a marketing line.
The site is served as static files from a CDN. There is no application server, no database, and no file-handling backend to breach – by design, we have built nothing that could receive your books even by accident.
About those converter-site warnings
In 2025 the FBI's Denver field office warned publicly about free online file converters that use the upload step to deliver malware or quietly harvest the contents of documents – including personal and financial information. The warning is worth reading even if you never use this site: any service that takes your file onto its servers can, by definition, do whatever it likes with it, and you're trusting that it won't.
A no-upload converter answers that fear structurally. Your file can't be harvested by a server that never receives it. That's the entire reason ebook.tools is built this way.
Where we draw the line: DRM
ebook.tools does not remove DRM, ever. When you drop a DRM-protected book (most Kindle and Kobo store purchases), we detect the protection and tell you plainly instead of producing a corrupt file. If you bought the book, check whether the store offers a DRM-free download – many indie stores and technical publishers do – or whether the publisher sells one elsewhere. The tools here are for the enormous world of DRM-free books: your own manuscripts, public domain libraries, indie purchases, and formats stranded on old devices.
ebook.tools vs the alternatives
| ebook.tools | Upload converters | Calibre | |
|---|---|---|---|
| Files stay on your device | Yes – provably | No – uploaded to their servers | Yes |
| Works with no install | Yes | Yes | No – desktop app |
| Works offline | Yes – after first visit | No | Yes |
| Speed on big files | Instant start, local speed | Upload + queue + download | Local speed |
| Free without limits | Yes, no caps or tiers | Usually capped or paid | Yes |
| Library management | No – conversion tools only | No | Yes – its real strength |
Honest summary: if you want a full library manager, install Calibre – it's excellent. If you want this one file converted now, privately, on any device you happen to be holding, that's what ebook.tools is for.