.fb2 File Extension

What kind of file is an .fb2?

An .fb2 file is a FictionBook 2 ebook. Unlike EPUB, it is one XML document rather than a ZIP package of web files. Its elements describe book-specific structure such as chapters, paragraphs, poems, quotations, notes, links, metadata, and images. A reading app chooses the fonts, margins, colors, and pagination for the screen.¹

The usual MIME type is application/x-fictionbook+xml. It is a widely used convention, not an IANA-registered media type.² FB2 has no fixed magic bytes because the XML declaration, encoding, comments, whitespace, and byte-order mark can vary. To verify a file, check for well-formed XML whose FictionBook root uses this namespace:

http://www.gribuser.ru/xml/fictionbook/2.0

How do I open an .fb2 on my computer?

• Windows, macOS, or Linux: open the book with FBReader or calibre.
• Android or iOS: use FBReader or another ebook app that explicitly lists FB2 support.
• Web browsers: a browser may display the XML source, but it will not normally provide a polished, reflowable book interface.

FBReader lists both raw fb2 and compressed fb2.zip support across desktop, Android, and iOS.³ calibre can read and convert FB2 on Windows, macOS, and Linux.⁴

If a reader rejects the file, confirm that it contains valid XML in the FictionBook namespace. A ZIP-compressed book is a different outer format, commonly named .fb2.zip or .fbz, and should not be treated as raw XML.

Poly support for .fb2

Poly gives valid FB2 ebooks a thumbnail, a paginated in-app preview, full-text and semantic search, and page-level content search. The Poly agent can read the book's extracted text and rendered pages after processing succeeds.

The preview uses fixed pages, so it does not behave like a native reflowable ebook reader. Open the original in FBReader or calibre when you want to change typography, margins, or responsive pagination. Damaged, malformed, encrypted, or unsupported books may not receive document features.

History of .fb2

Dmitry Gribov's FictionBook 2 schema dates to 2004.¹ Its design emphasizes the meaning and organization of a book instead of its final page layout. The schema can record authors, title, language, publication data, revision history, nested sections, poetry, notes, and Base64-encoded images in a single XML file.

The format became established particularly in FictionBook-oriented libraries and readers. It remains in active software support even though application/x-fictionbook+xml was never added to the IANA registry.²³

Working with .fb2 and alternatives

calibre can convert an unprotected FB2 book to EPUB or PDF. Review the cover, chapter order, table of contents, footnotes, poetry indentation, images, language metadata, and non-Latin text afterward. Conversion can change presentation, especially when moving from a reflowable XML book to fixed PDF pages.⁴

Keep the source .fb2 so future conversions start from the original semantic structure. Treat files from unknown sources as untrusted XML, use a maintained reader, and keep external-resource loading disabled if you configure an XML parser yourself.⁵