What is an FB2 file?

FB2 is a plain-text format you can open in any editor. It is used for handing a finished file over.

The extension is .fb2, and the full name is FictionBook 2. Both matter less than what the file can hold, which is what the rest of this page is about.

It dates from 2004.

Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.

It is published in full, so anyone can implement it from the document rather than by inspection, which is why it turns up in so many programs and why files written twenty years ago still open. A published specification is not the same thing as a royalty-free one: where a format wraps a codec, the patent licensing is a separate question the standard does not settle.

It exists to do one job well for one group of people. Outside that job it is a poor default, and inside it there is usually nothing better.

FB2 is not limited to one page, which matters when converting to something that is: one conversion produces one file holding a single page — the first one, unless the page is something the converter lets you pick.

Calibre and FBReader read it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

No browser reads it.

That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.

FB2 is meant to be opened and changed. Keep the file in this format for as long as the work is going on, and export from it whenever a finished copy is needed.

An FB2 file is a single XML document containing the entire book: the metadata, the text with its chapter structure, and any illustrations encoded as base64 inside the same file. There is no archive, no folder, no manifest — open it in a text editor and the whole novel is there, marked up.

That is the deliberate difference from EPUB, which is a ZIP holding many HTML files and a set of index documents. One file is easier to store, to copy and to hand around, and it cannot be half-corrupted by a broken archive. It is also, for a book of any size with pictures, considerably larger than the zipped equivalent.

FictionBook marks up what things are: a chapter, an epigraph, a poem with its stanzas and lines, a verse, a citation, a subtitle. It does not say what any of it looks like — no fonts, no margins, no page layout, no styling of any kind.

This is a genuine design position rather than an omission, and it comes from the format’s origin among people digitising literature. The reader decides typography; the file describes the book. A poem tagged as a poem stays a poem when a reading application reflows it onto a phone screen, which is precisely what a file of manually formatted line breaks would not do.

Russia and the wider Russian-speaking world, overwhelmingly, and to a lesser extent elsewhere in Eastern Europe. It emerged in the early 2000s from large volunteer libraries digitising fiction, and it stayed because it fitted that work well: one file per book, structural markup that survives conversion, and a metadata section describing the author, translator, series and genre in a way a library catalogue can use.

Outside that world it is rare, which is the entire reason this page exists. The usual encounter is somebody downloading a book from a Russian-language library and finding that neither their e-reader nor their phone will open it.

Calibre opens FB2 directly and is the most practical answer on a desktop, since it also converts and manages a library. Several Android reading applications support it natively — the format is common enough in that market that most serious readers do.

What generally does not read it is an Amazon Kindle, an Apple Books library, or a browser. For those, conversion is not a preference but a requirement, and it is what most people end up doing.

EPUB is the natural target: both formats describe structure rather than appearance, so chapters stay chapters, the table of contents survives, and images come across. The conversion is one structural vocabulary into another, which is about as clean as document conversion gets.

What tends to be approximated is the more literary markup. Poetry, epigraphs and citations have precise tags in FictionBook and only loose equivalents in EPUB, so they usually arrive as styled paragraphs — visually reasonable, structurally flattened. For a novel that is invisible; for a volume of verse it is worth checking a page before committing the whole library.

The description section at the top of the file carries more than most e-book formats bother with: author with given, middle and family names separated, translator, original language, series and the number within it, genre from a controlled list, and the history of who produced the file and when.

This matters when converting a collection. A conversion that maps those fields properly gives you a library that sorts and groups correctly; one that does not gives you four hundred books all filed under a mangled author name. It is worth checking the first few results rather than the last.

Files often arrive as .fb2.zip or .fbz, which is exactly what it sounds like: the same XML compressed. Since the format is verbose text with base64 images, compression is dramatic — often to a fifth of the size — and most tools that read FB2 read the zipped form directly.

If something refuses it, unzipping first gives you the plain .fb2 and costs nothing. There is no difference in content between the two, and nothing is lost in either direction.