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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.