OPF (ebook package)
Also known as: .opf file, Open Packaging Format, EPUB package file
OPF (Open Packaging Format) is the XML manifest at the heart of an EPUB ebook. It lists every file in the book, sets the reading order, and stores metadata like title and author — the table of contents the reader software follows.
- XML manifest inside an EPUB ebook
- Lists files, reading order, and metadata
- Tiny text file; central to EPUB structure
What the OPF does
Inside an EPUB (which is itself a ZIP), the .opf file is the master manifest. It declares the metadata (title, author, language), lists all content files in the manifest, and defines the spine — the order pages are read in.
Because OPF is XML, you can open it in a text editor to see exactly how a book is assembled. Calibre and other ebook tools also produce standalone .opf files to store a book’s metadata.
When you see OPF on its own
Ebook managers often save a .opf next to a book to hold its metadata and cover info separately. It is a tiny text file, not the book content itself.
You rarely edit OPF by hand. It matters mainly when you are building or repairing an EPUB and need to fix the manifest or reading order.