Boko is a fast ebook converter for EPUB, KFX, AZW3, and MOBI, written in Rust.
KFX renders with hyphenation, kerning, and ligatures. AZW3 doesn't. MOBI (Calibre's default Kindle format) is 25 years old at this point. boko is the only KFX writer that doesn't run Amazon's proprietary Kindle Previewer software. It's 2026, use boko to send .kfx files to your Kindle!
Browser app: https://zacharydenton.github.io/boko. Converts ebooks in your browser, fully client-side.
| Format | Read | Write |
|---|---|---|
| KFX | yes | yes |
| AZW3 | yes | yes |
| EPUB 2/3 | yes | yes |
| MOBI | yes | no |
| Markdown | no | yes |
| Plain text | no | yes |
Requires Rust 1.85+.
cargo install boko # CLI
cargo add boko # library
boko convert in.epub out.kfx
boko convert in.epub out.azw3
boko convert in.kfx out.epub
boko info in.epub
boko info --json in.epub
boko dump in.epub
boko dump -c 0 in.epub
kfx-dump is installed alongside boko.
use boko::{Book, Format};
use std::fs::File;
let mut book = Book::open("in.epub")?;
let mut out = File::create("out.kfx")?;
book.export(Format::Kfx, &mut out)?;Full API: https://docs.rs/boko
Format → semantic IR → format. Imports compile to an intermediate representation: nodes, computed styles, semantic roles, metadata, TOC. Exporters render IR back out.
EPUB ─┐ ┌─ EPUB
KFX ─┼─→ semantic IR ─→─┼─ KFX
AZW3 ─┤ ├─ AZW3
MOBI ─┘ └─ Markdown / text
Bug reports with sample files welcome, especially KFX and AZW3 edge cases.
cargo test
cargo clippy -- -D warnings
cargo fmt --check