.fbz File Extension

What kind of file is an .fbz?

In ebook collections, an .fbz file is usually a ZIP-compressed FictionBook 2 book. The archive normally contains one .fb2 XML document with the book's chapters, metadata, notes, and Base64-encoded images. Compression reduces storage and transfer size without changing the FictionBook vocabulary.

The associated MIME type is application/x-zip-compressed-fb2. It is a software convention, not an IANA-registered media type.¹ An FBZ archive commonly begins with the ZIP local-file signature 50 4B 03 04, but those bytes identify many ZIP-based formats. Confirm that the archive contains an .fb2 member whose XML root is FictionBook in the FictionBook 2 namespace.²³

How do I open an .fbz on my computer?

• Windows, macOS, Linux, Android, or iOS: FBReader supports ZIP-compressed FB2 books across its desktop and mobile editions.⁴
• Windows, macOS, or Linux: calibre can read FictionBook content and convert it to formats such as EPUB or PDF.⁵
• Linux: Foliate advertises support for the compressed-FB2 MIME type.⁶

A web browser normally downloads an FBZ or exposes it as an archive rather than presenting a polished ebook. If a reader rejects the file, inspect it with an archive utility. A valid compressed book should contain readable FictionBook XML and should not require a password.

Poly support for .fbz

Poly recognizes .fbz as a compressed FictionBook ebook. For a valid book, Poly provides a thumbnail, a paginated in-app preview, full-text and semantic search, and page-level content search. The Poly agent can read the extracted text and rendered pages after processing succeeds.

The preview uses fixed pages, so it does not reproduce the responsive typography of a native ebook reader. Encrypted, damaged, malformed, or unrelated .fbz files may not receive document features.

History of .fbz

FictionBook 2 dates to Dmitry Gribov's 2004 XML schema.³ The .fbz convention did not introduce a new book format. It packaged the existing XML document in ZIP compression for smaller distribution.

Desktop MIME databases later standardized a practical identifier for the compressed form. The freedesktop.org definition treats application/x-zip-compressed-fb2 as a subtype of ZIP and looks for an .fb2 member inside the archive.² The exact origin date of the shorter .fbz spelling is not established by an open specification.

Working with .fbz and alternatives

Extracting the enclosed .fb2 preserves the original book data. Converting to EPUB or PDF is a transformation, so review the cover, chapter order, table of contents, notes, poetry indentation, images, and non-Latin text afterward. Keep the source FBZ if future conversions matter.

Treat unknown archives as untrusted. Preview member names and declared sizes before extraction, reject unsafe paths, and use maintained ebook and archive software.