What is an OPF file in EPUB?

The OPF (Open Packaging Format) file is the package document that ties an EPUB together. It contains three main sections: metadata (title, author, language), manifest (list of all files), and spine (reading order). Every EPUB must have exactly one OPF file, referenced from META-INF/container.xml.

What must be in the EPUB 3 OPF metadata?

EPUB 3 requires three dc: elements (identifier, title, language) plus a dcterms:modified meta element with an ISO 8601 UTC timestamp. Accessibility metadata using schema.org properties is strongly recommended.

What is the EPUB spine?

The spine element in the OPF lists HTML document items in reading order using itemref elements. Items marked linear='no' (like cover pages and TOC) are not part of the sequential reading flow.

Where is the OPF file located in an EPUB?

Its location varies — typically OEBPS/content.opf or OPS/package.opf — but the actual path is always declared in META-INF/container.xml via a rootfile element. Reading systems always check container.xml first.

EPUB OPF Package Document: Structure, Metadata, and Spine Explained

June 12, 2026 · 8 min read

Contents

What is the OPF document?
Metadata section
Manifest section
Spine section
EPUB 3 changes
FAQ

Every EPUB file contains a package document — an XML file with a .opf extension (historically called content.opf or package.opf) that ties the whole ebook together. Reading systems parse it first to understand the book's structure. This guide explains each section and what EPUB 3 changed from EPUB 2.

What is the OPF document?

OPF stands for Open Packaging Format. It's an XML file inside the EPUB archive that answers three questions for the reading system:

What is this book? (metadata — title, author, language, UUID)
What files does it contain? (manifest — every resource listed)
In what order should the content be read? (spine — reading order)

A minimal EPUB 3 OPF document:

<?xml version="1.0" encoding="UTF-8"?>
<package xmlns="http://www.idpf.org/2007/opf"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         version="3.0"
         unique-identifier="bookid">

  <metadata>
    <dc:identifier id="bookid">urn:uuid:a1b2c3d4-e5f6-7890-abcd-ef1234567890</dc:identifier>
    <dc:title>My Book Title</dc:title>
    <dc:language>en</dc:language>
    <dc:creator>Author Name</dc:creator>
    <meta property="dcterms:modified">2026-06-12T00:00:00Z</meta>
  </metadata>

  <manifest>
    <item id="nav"   href="nav.xhtml"      media-type="application/xhtml+xml" properties="nav"/>
    <item id="ch01"  href="chapter01.xhtml" media-type="application/xhtml+xml"/>
    <item id="ch02"  href="chapter02.xhtml" media-type="application/xhtml+xml"/>
    <item id="style" href="style.css"       media-type="text/css"/>
    <item id="cover" href="cover.jpg"       media-type="image/jpeg" properties="cover-image"/>
  </manifest>

  <spine>
    <itemref idref="nav"  linear="no"/>
    <itemref idref="ch01"/>
    <itemref idref="ch02"/>
  </spine>

</package>

Metadata section

The <metadata> element uses Dublin Core elements (prefixed dc:) for the core bibliographic fields:

Element	Required?	Notes
`dc:identifier`	Yes	Must match `unique-identifier` on `<package>`; use UUID or ISBN
`dc:title`	Yes	Book title; repeat for subtitle with `title-type` refinement
`dc:language`	Yes	BCP 47 code (e.g., `en`, `fr`, `zh-Hans`)
`dc:creator`	Recommended	Author; use `role` refinement for editor, illustrator, etc.
`dc:publisher`	Optional	Publisher name
`dc:description`	Optional	Synopsis / back-cover copy
`dc:subject`	Optional	Repeat for multiple subjects/categories
`dc:date`	Optional	Original publication date
`meta property="dcterms:modified"`	Yes (EPUB 3)	ISO 8601 UTC timestamp; must update on each revision

EPUB 3 also supports accessibility metadata via meta elements with schema.org properties:

<meta property="schema:accessMode">textual</meta>
<meta property="schema:accessMode">visual</meta>
<meta property="schema:accessibilityFeature">structuralNavigation</meta>
<meta property="schema:accessibilityHazard">none</meta>
<meta property="schema:accessibilitySummary">This publication meets WCAG 2.2 Level AA.</meta>

Manifest section

Every file in the EPUB must appear in the manifest — HTML chapters, CSS, images, fonts, the nav document, and the NCX (if included). Each <item> has:

id — unique identifier within the OPF (used by spine idref)
href — relative path from the OPF file
media-type — MIME type of the resource
properties — optional flags: nav, cover-image, scripted, mathml, svg

Common media types:

File type	media-type
XHTML content	`application/xhtml+xml`
CSS	`text/css`
JPEG image	`image/jpeg`
PNG image	`image/png`
SVG	`image/svg+xml`
OTF font	`font/otf`
WOFF2 font	`font/woff2`
NCX	`application/x-dtbncx+xml`
Nav document	`application/xhtml+xml` + `properties="nav"`

Spine section

The <spine> defines the default reading order. Each <itemref> references a manifest item by its id:

<spine>
  <itemref idref="nav"   linear="no"/>
  <itemref idref="cover" linear="no"/>
  <itemref idref="ch01"/>
  <itemref idref="ch02"/>
  <itemref idref="ch03"/>
</spine>

The linear="no" attribute marks items that are not part of the linear reading flow (cover page, table of contents). Readers may skip them in sequential navigation.

Key changes in EPUB 3

Nav document replaces NCX — the manifest must include an item with properties="nav".
dcterms:modified is required — must be present and updated on every revision.
Media overlays — new media-overlay attribute on manifest items for read-aloud sync.
Accessibility metadata — schema.org properties are now standard practice.
Guide element removed — the EPUB 2 <guide> element is replaced by the landmarks nav in EPUB 3.

FAQ

Where is the OPF file located inside an EPUB?

The META-INF/container.xml file (required in every EPUB) points to the OPF file's location with a rootfile element. The OPF is typically at OEBPS/content.opf or OPS/package.opf, but the path is not fixed.

Can an EPUB have multiple OPF files?

In EPUB 3, no — only one rendition (one OPF) is supported. EPUB 3.0.1 added multiple renditions as an experimental feature, but it was never widely implemented and was removed in EPUB 3.2.

What happens if a file is in the EPUB zip but not in the manifest?

EPUBCheck will report an error. Reading systems may ignore the file entirely. Every resource referenced from content must be in the manifest.

Do I need a spine entry for every manifest item?

No. CSS, images, fonts, and the nav document do not need spine entries. Only the HTML documents that form the reading sequence belong in the spine.

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