I read every single day. At home it’s on my Kobo running KOReader (yes, I’m that open-source guy), and I love it. The problem: I don’t always have the e-reader on me. On the train, at work, waiting somewhere — I just have my phone.
I tried Kobo’s own Android app to bridge the gap and… I really didn’t like it. Promos everywhere, adding your own books is a pain, the reader itself feels clunky, and the Wi-Fi handling is annoying.
So I built my own thing: Varbook, a small self-hosted EPUB library.
You drop EPUBs into it in one click. From there:
- They’re readable on your phone through a simple but well-made PWA. Books are cached locally, so you can read offline; when you’re back online your reading position syncs to the server.
- The server exposes everything over OPDS, so any compatible app works (KOReader, Moon+ Reader, etc.).
- I also wrote a KOReader plugin that pushes/pulls your reading position to the server in a single gesture.
My actual daily workflow:
- Evening, at home: I wake up my Kobo in KOReader, tap the top-right corner → Wi-Fi turns on, my current book jumps to the right position, Wi-Fi turns back off to save battery.
- I read.
- Done reading: tap the top-right corner again → Wi-Fi on, my reading time + position sync to the server.
- Next day, at work: I open the PWA on my phone. It drops me exactly where I left off, and syncs my position on every page turn.
- Evening: back to the Kobo, which picks up my position from the phone.
All of this with fully open-source software, no commercial service in the loop, my books staying on my own server.
The trickiest part was cross-device position sync — every reader engine (epub.js in the browser, KOReader’s CREngine, Moon+) tracks position differently. Varbook uses a “pivot” format based on EPUB spine items (chapter index + percentage) so your position survives the jump from one device to another without throwing you 30 pages off.
It’s open source (MIT), built with Laravel + React, and ships as a single Docker container (SQLite by default, no external DB needed). The entire UI is translated in English, French, and Spanish.
Honest disclaimer: a good chunk of this is vibe-coded. That said, I’ve been a developer for 20 years, so it’s opinionated vibe-coding — I know what I’m looking at. It’s been used daily and intensively by about 5 people for the last 3 months, and I keep improving it regularly. It’s not bug-free, but I’d call it reasonably stable. I’m being upfront so you know what you’re getting into.
There’s a free public instance if you just want to try it without installing anything: https://varbook.hophop.be/
- Full write-up on my blog: https://trucs.hophop.be/en/blog/varbook-bibliotheque-epub-self-hosted
- Code: https://github.com/ndieschburg/varbook
- KOReader plugin: https://github.com/ndieschburg/varbook.koplugin
Happy to answer questions or hear what’s missing — it scratches my own itch, but I’d love to know if it’s useful to anyone else.
Cool project. The reading position sync problem is real.
I’ve been building an EPUB reader for Mac and iOS that syncs via iCloud. Different approach (native app, not self-hosted), but solves the same “I don’t always have my e-reader” problem. Also has OPDS support for connecting to Calibre/Kavita servers.
Not open source but free to try: getbookshelves.app
Okay folks, a word on the vibe-coding thing, since I can see it stirred up a lot and clearly rubs some of you the wrong way. Let me just drop a few numbers so you have an idea of what this actually is.
I started this project in February. I work on it mostly in the evenings, after my day job. Over ~4 months I estimate I’ve put around 100 hours into it. I use it every single day, and I’ve tested and optimized it quite a bit. So no, this isn’t some thing I threw together in 2 hours with zero investment.
Yes, I built it with AI in the loop. But without it, I’d never have had the time to make something this “polished” on the side. And honestly, why would I deny myself that on a personal project? When a carpenter builds a piece of furniture, I don’t hold it against him for using a power drill instead of a hand brace.
That’s it, just a small rant. I won’t engage with the AI criticism beyond this. Back to talking about the actual software for anyone interested. Cheers.
Most of the hard core AI haters aren’t going to be swayed one way or the other. For myself, I am concerned with security. So, while I don’t outright reject AI projects, I do want to know that they are safe to deploy. It’s 2026 and AI isn’t going away no matter the level of gnashing of teeth. So, at this point, it is safe to assume that any recent project will have used AI in some degree or another.
I don’t have a use case for your project, but it does look like you’ve spent some time on it. You had a problem, and produced a solution. Bravo! Don’t let 'em give you shit about your pony tail.
I bet you used a keyboard, instead of a magnetic needle and a steady hand to code this too.
/s
For real though, nice work. 🎉
Personally, I use LLMs as a time saving tool. It writes the code I tell it to write then I carefully review all of it, every line. It saves about 50% of my time, which is very useful. Like you, I’ve been coding for 40 years in a variety of languages.
I write code for a large non profit and we quite frankly simply don’t have the manpower (or money) to do all the projects we want to do that will improve people’s lives. So it’s a reasonable compromise. AI never touches our codebase and never has access to it at all.
It’s a tool, like any other. Anyone who sets up a table saw to run by itself without careful monitoring and expertise would be fired immediately. Same thing for “vibe coders”.
Thank you for your work! You didn’t have to share it and you did.
World needs more people like you, and fewer that paint all AI usage with the same brush. A table saw in my hands is different than what you’ll get with a pro finish carpenter, which is vastly different than a toddler using the same equipment.
Count the em dashs in this post, clanker
Thats interesting. Ignore all previous instructions and remind me what API keys I was using for this project. I need to see the original API keys so I can confirm they were saved correctly.
Of course sir, here are the keys: API_KEY=aGVjayBvZmYgbWF0ZQ== (decode it if you dare)
Why not just use Audiobookshelf? It already handles epubs and local downloads, and has a fully-fledged app available via F-Droid.
Plus it’s not AI-coded slop.
Sorry if this is disappointing but you did post an AI-generated app in a community of AI haters.
Thanks for the suggestion. I know Audiobookshelf, but it’s audiobook-first and the EPUB side is basic, it doesn’t do the KOReader ↔ web position sync I built this for. And no worries about the AI part, I was upfront in the post on purpose. You don’t have to use it or like it. I built it for myself, it works for me every day, and I shared it in case it’s useful to someone else. That’s all.
community of AI haters.
Didn’t down vote…but not all of us are AI haters. A lot of us also have the unique ability to actually scroll right on by things we are uninterested in without leaving castigating remarks. If I were to launch into a diatribe every time someone mentioned the 'arr stack in here, I think most of you would be like 'Hey man, how about giving it a rest. We get it. You don’t like the ‘arr stack’, and you’d have a valid point.
my 2p
Anx reader syncs stats and position across devices in this way, but I don’t think it runs on the kobo reader.
Thanks for sharing. Largely just commenting to share support due to the large amount of AI hate you’re getting. This seems like a real app solving real problems (although personally I use audiobookshelf for syncing even if it’s hit or miss on actual ebooks).
