FB2 → MOBI/AZW3
Converting a novel from FictionBook (.fb2) to Kindle / Mobipocket (.mobi, .azw3, .azw) is a routine step in practice — the Kindle format reads natively on Amazon devices and apps, and can be delivered with Send to Kindle. Fortunately FictionBook and Kindle / Mobipocket are structurally close, so there is not much to lose. Below we explain in detail how FictionBook becomes Kindle / Mobipocket and what to watch out for, and the page ends with a converter that does the job right in your browser — nothing is uploaded, the file never leaves your machine.
What is FB2?
FB2 (FictionBook) is an open e-book format based on XML. Text, metadata and illustrations all live in a single file, with images embedded as Base64, so one file distributes completely and you never end up with the text present but the images missing. Its structure is simpler than EPUB and therefore easier for readers to implement, and it is most popular in Russian-speaking regions. The drawback is that it supports almost no complex CSS, so it suits text-plus-illustration books rather than titles that depend on fine layout. Read the FB2 format guide
| Extensions | .fb2 |
|---|---|
| Typical use | Russian-language e-books; single-file distribution where embedded illustrations and full metadata matter. |
What is MOBI/AZW3?
The Kindle family (.mobi, .azw3, .azw) is Amazon's proprietary e-book format. It reflows and can carry a table of contents, and it is read mainly on Kindle devices and the Kindle app, or delivered through Send to Kindle. AZW3 supports a reasonable amount of CSS while the older .mobi barely supports any. It is one of the most common proprietary formats in existing libraries — plenty of books bought or downloaded years ago are in it — which is why converting it to something more portable is such a practical need. Read the MOBI/AZW3 format guide
| Extensions | .mobi.azw3.azw |
|---|---|
| Typical use | Reading on Kindle devices and the Kindle app; one of the most common proprietary formats in existing libraries. |
How to convert FB2 to MOBI/AZW3
FB2 is a single XML file with Base64-embedded images. Parsing must handle the XML namespace and <binary> nodes; ignoring them silently drops every image. Base64 also makes the file roughly a third larger than an equivalent EPUB.
Producing .mobi/.azw3 requires Amazon's toolchain or Calibre. AZW3 supports reasonable CSS while legacy .mobi supports very little; for newer devices, target AZW3 — or simply deliver an EPUB.
Convert FB2 to MOBI/AZW3
FB2 → KINDLE
The Kindle formats (.mobi, .azw3, .azw) are Amazon's proprietary binary containers with no public specification, so they cannot be reliably parsed or produced in a browser. This direction needs a desktop e-book tool; the EPUB or TXT you convert can be read in the Kindle app directly.
A novel reader that syncs your progress across every platform
Tide Reader opens TXT and EPUB, detects chapters on import, lays the text out the way you like it, and syncs your reading position across Windows, macOS, iOS and Android. Drop the converted file in and start reading.
Download Tide ReaderTXT and EPUB; local-first reading, with optional cloud sync and WebDAV.