How to edit EPUB metadata, and why series information gets ignored

An EPUB is a ZIP archive with rules

Rename any .epub file to .zip and you can open it. Inside you will find the book’s chapters, images, stylesheets and fonts — plus two small XML files that do the structural work. META-INF/container.xml is the entry point: it names the package document, usually something like OEBPS/content.opf. The package document, called the OPF, is where the book’s identity lives: title, author, language, identifiers, cover, and — for anyone with a series — the series name and number.

That file is why metadata edits are safe to do by hand. Nothing about the story changes. You are adjusting a description of the book, not the book.

Where series information actually lives

There is no single, universally honoured place for “this is book two of the Silver Pines series”. In practice, two encodings matter.

The first is the EPUB 3 way. The metadata section contains a meta element with property="belongs-to-collection" holding the series name, and a second element that refines it, property="group-position", holding the number. This vocabulary is defined in the EPUB 3 specification, which the W3C published as a Recommendation (EPUB 3.3, January 2026). It is the encoding a standards-compliant reader is expected to understand.

The second is the calibre way. Long before EPUB 3 existed, calibre — the most widely used ebook manager — began writing series data as meta elements namedcalibre:series and calibre:series_index. A decade and a half of books carry exactly these fields, and a long list of tools and reading systems still look for them first.

This is the practical trap: a book can have one encoding and not the other. A tool that only understands calibre fields sees nothing in a clean EPUB 3 file; a reader that only understands EPUB 3 sees nothing in an older book. The safe answer is to write both at once, which is what EpubMeta does, and what calibre itself does when it updates a book’s metadata.

Why sideloaded books so often show no series

A book bought from a store arrives with the store’s own catalogue data attached, and that is what the reading system uses for series shelves and “next in series” prompts. When you sideload a file — copy it onto the device yourself — there is no catalogue entry, only the file. Everything the device knows about the book has to come from inside the EPUB itself.

What happens next depends on the device. Kobo models read series information for sideloaded books in many firmware versions, and it is the calibre-style fields they respond to in most of those cases; a re-import or database rescan is often needed before the series appears. Kindle reading systems, by contrast, generally do not use the series metadata inside a sideloaded EPUB at all — series grouping there is built from Amazon’s catalogue, so a sideloaded book typically stays out of the series no matter how correct the file is. That is a platform decision, not a file defect.

The honest summary: correct series metadata is necessary for a sideloaded book to be grouped, but on some devices it is not sufficient. Fixing the file is still the only part you control, and it is the part that travels — the same corrected EPUB behaves correctly in apps like calibre, Thorium, KOReader and others that read the OPF directly.

Fixing it without installing anything

The traditional route is calibre on a computer: import the book, edit the metadata, save it back. That works well at a desk. If the book is on your phone, there is a shorter route:

1. Open the EpubMeta editor in the phone’s browser.
2. Choose the EPUB — from Downloads, a cloud folder, wherever it lives.
3. Fill in the series name and index, and correct anything else that is wrong: title, author, language, publisher, ISBN, description, cover.
4. Save. The edited file is rebuilt, re-opened and checked inside the page, then downloaded. Nothing is uploaded at any point.

The saved file keeps mimetype as the first ZIP entry, stored uncompressed, exactly as the format requires — that detail is what many tools and reading systems use to recognise a valid EPUB at all. Every other file in the book is copied through unchanged.

Check your work

After saving, sideload the edited file and check what the device shows. If the series still does not appear, the usual causes, in order: the device has not re-scanned its library (eject and reconnect, or trigger a library refresh); the device simply does not read series metadata for sideloaded books (common on Kindle); or the series fields are still wrong in the file — re-open it in the editor and look at what it reads back.

For a stricter check than any editor’s built-in checks, run the saved file through epubcheck, the community’s reference conformance checker. EpubMeta’s own checks are a structural subset — package document parses, spine and manifest agree, referenced files exist, mimetype ordering is right — and they are described that way on purpose. They catch the mistakes this tool could introduce; epubcheck catches everything else.

Sources

• W3C, EPUB 3.3 Recommendation (January 2026), metadata vocabulary includingbelongs-to-collection and group-position:w3.org/TR/epub-33.
• calibre user manual, “Editing e-book metadata” — series is a first-class field in calibre’s metadata model:manual.calibre-ebook.com/metadata.html.

Device behaviour differs by model and firmware version, and it changes with updates. The statements here are the conservative reading of long-standing, widely reported behaviour; where a claim depends on your specific reader, test it with one book before you fix a hundred.