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Colophon repairs ebook files in your browser. See what's inside an EPUB, fix wrong titles, authors and series, learn why a cover won't show on your Kindle, and clean up text a bad conversion broke. You approve every change. No account; files gone in an hour.
Hi Product Hunt! 👋
I'm an independent full-stack developer, and Colophon is a project I built for people who read ebooks on Kindle, Kobo, PocketBook, or any other e-reader.
It started as a university project, but it quickly became something I kept using myself. Most EPUB problems aren't about the book — they're small faults hidden inside the file: a cover that won't show, wrong metadata, a series that won't group, or text damaged by a bad conversion.
Fixing them usually meant opening a heavyweight desktop app for a job that should take a minute.
So I built the simple version.
What Colophon does
Check File — reads an EPUB and explains what's inside: EPUB version, DRM or font obfuscation, metadata, images, fonts, archive structure, and where the file size goes.
Edit Book Info — edit the title, author, author sort, series, ISBN, publisher, language, description, and cover. It opens EPUB, AZW3, MOBI, and FB2 and writes the changes into the book itself, so they survive copying to any device — unlike edits made only in a library app.
Fix Cover — checks the nine most common reasons a cover appears on your computer but not on your Kindle (camera metadata, print color profile, progressive JPEG, and more) and repairs only the issues you choose.
Fix Text — finds encoding damage (don’t), lookalike letters from another alphabet, invisible characters, spacing issues, and repeated words. Every change is previewed in context, and nothing is applied until you approve it.
Send to E-reader — email the finished book directly to Kindle or PocketBook.
Telegram bot
There's also a Telegram bot (@colophon_tools_bot) for when the book is already on your phone. It can convert books to EPUB, edit the title, author, or cover, and send the finished book straight to your e-reader.
How it works
Everything runs in the browser:
No account.
Nothing to install.
Uploaded files get random names and are deleted after an hour.
It's free for 15 books a day. After that, a one-time pack of 50 fixes costs $5 — no subscription.
One thank-you
Every conversion and metadata update in Colophon is powered by Calibre's command-line tools. Colophon stands on more than twenty years of work by Kovid Goyal and the Calibre project.
P.S. I'd love to know: what's the most annoying EPUB problem you've run into? That's what will help me decide what to build next.
Dial
the DRM/font obfuscation detection in Check File is the part I didn't expect from a browser tool, that's usually where people give up and just accept a broken cover. the no-account, files-gone-in-an-hour angle also makes sense for something people use maybe once every few months rather than daily, no reason to make someone sign up for that. did the university-project version already have the approve-every-change flow, or did that come later once real users started sending you weirder files than you'd tested against?
@galdayan Thanks! That was actually one of the first features I wanted in Check File, because I kept running into books that looked "broken" for reasons that weren't obvious at all.
The approve-every-change flow came later. The university version was much simpler and mostly applied fixes automatically. Once I started testing a much wider variety of EPUBs, I realized "fixing" can sometimes change something the reader actually wanted to keep, so now every text or cover change is previewed and opt-in.
Dial
@ianciuc_nadejda that makes sense, and honestly it's the more trustworthy design. an automatic-fixer that silently rewrites your file is the kind of thing that breaks a reader's confidence in the tool after one bad experience. for the preview step, do you show a plain before/after diff per change, or is it more like a checklist of "these N things look broken, want them fixed"? curious how much detail you expose without turning it into something that takes longer to review than just re-downloading the book
@galdayan Exactly - I didn't want the review to become another job in itself. For text, Colophon only shows the sentences where it found a problem, with the suggested correction right there, so you can quickly accept, skip, or edit it yourself.
For covers, it's even simpler: you get a list of the specific problems it found and choose which ones to fix.
So you're reviewing only the changes Colophon wants to make, not the whole book.