EPUB FixerKDP upload error scanner

EPUB error guide

EPUB metadata checker

Use this when content.opf has a metadata or file-list error, including identifiers, modified date, incomplete manifest items, duplicate entries, missing feature properties, or media:duration totals.

Change the EPUB title, author or language with the separate metadata editor.

Scan EPUB structureSee an example report

Scan the EPUB to check file paths and see what can be repaired or needs manual review. Your original EPUB stays unchanged.

No signup before the scan report.Your original file is not overwritten.Repair download only after EPUBCheck passes again.

Need fixed-layout, DRM, or source-file help? Check unsupported or review-first EPUB cases.

Match these report titles

  • EPUB metadata check
  • OPF metadata error
  • Unique identifier or dc:identifier problem
  • EPUB manifest item is missing id
  • EPUB manifest item is missing media-type
  • Duplicate OPF manifest item
  • Manifest item is missing scripted, svg, mathml, or switch property
  • MED_016 package media:duration does not match the sum of the Media Overlays
  • RSC_005 package media:duration is missing or malformed
  • EPUB package metadata blocker

Start here

Check OPF metadata structure, not marketing metadata.

This guide checks content.opf structure and package fields used by EPUBCheck. If you want to change the book title, author or publication language, use the separate EPUB metadata editor linked below.

Matched

What it means

EPUB metadata lives in the OPF package document. Validators check whether required fields exist and whether package fields point to real metadata entries.

Matched

Can it be fixed automatically?

A checked repair is possible when the existing package proves one exact OPF change, including an identifier link, modified timestamp, item attribute, feature property, redundant duplicate, or package duration total calculated from a complete unique set of valid per-SMIL durations.

Matched

What to check next

Find the OPF file path from the EPUB package or report.

Matched

What not to assume

It does not choose competing identifiers, rewrite sales metadata, infer narration timing from audio, invent missing per-SMIL durations, or decide publishing platform listing fields.

1. Example report output

What a metadata checker report should show.

A useful metadata report should name the exact OPF field, not just say metadata is wrong.

OPF file

Usually OEBPS/content.opf or another package document path from container.xml.

Metadata field

unique-identifier, dc:identifier, dcterms:modified, manifest item, or another package field.

Manifest structure

Whether an item is missing id, href, media-type, required feature properties, or appears more than once.

Read-aloud duration

Whether every unique SMIL item has one valid refined duration before the package-level total is calculated.

Validator signal

OPF_030, OPF_048, OPF_049, MED_016, RSC_005 duration, modified date, duplicate manifest item, missing attribute, or media-type message.

Decision

Repair when one required value or link is clear; review manually when several identifiers or source metadata values compete.

The report should tell you which OPF field to inspect before you change title, author, ISBN, or source metadata.

2. Next step

Choose metadata repair or source review.

Use the scan report to decide whether an OPF metadata problem is a simple wiring repair or needs the real book metadata.

Identifier

Use this when unique-identifier or dc:identifier fails.

Repair only when one real metadata id is clearly the intended package identifier.

Manifest item

Use this when a file-list entry is incomplete or duplicated.

A missing id or media-type, required scripted/svg/mathml/switch property, or proven redundant entry can be repaired only when the existing file provides one exact answer.

Read-aloud duration

Use this for MED_016 or a package media:duration RSC_005 message.

Correct the package total only when every unique SMIL manifest item already has exactly one valid refined duration. Missing, duplicate, or malformed per-SMIL values remain manual.

Manual review

Use this when multiple ISBN, UUID, retailer, draft, or source ids compete.

Do not choose an identifier just to clear the validator if the real book identity is unclear.

3. Concrete path example

An OPF metadata error often starts with a broken id link.

The package unique-identifier must point to a real identifier element.

EPUBCheck:
OPF_030: The unique-identifier "bookid" was not found.

Report:
Package field: unique-identifier="bookid"
Metadata ids found: uuid_id, isbn_id
Decision: manual review unless one id is clearly the intended book identifier

Do not change visible title or author fields to fix this. The broken link is inside OPF package metadata.

Quick decision

Decide whether metadata is missing, mismatched, or ambiguous.

Metadata checks are useful only when they lead to a specific OPF field and a safe next step.

Good fit

The OPF field or manifest item has one clear correction.

A unique-identifier link, modified date, item attribute, required feature property, redundant duplicate, or package duration total can be checked safely when the existing package proves the answer.

Manual fit

Several values could be right or duration evidence is incomplete.

The report can name the candidates or missing SMIL duration fields, but a person should supply the real metadata or read-aloud timing.

Not this tool

You want to edit retailer listings.

The title on a store's sales page, author bio, categories, keywords, pricing and retailer descriptions are managed in the publishing platform. Changing metadata inside your EPUB does not update those listings.

Common situations

Common EPUB metadata checker cases.

Start with the OPF field that the validator names.

Matched

unique-identifier points to a missing id.

The package tag names an identifier that does not exist in the metadata block.

Align only when one existing dc:identifier is clearly intended.

Matched

Language metadata is missing or unclear.

The EPUB needs a real language value for the book, not a guessed placeholder.

Add one clear value such as en, en-US, or another real language code when known.

Matched

dcterms:modified is missing or duplicated.

EPUB 3 files can fail when modified metadata is absent, duplicated, or malformed.

Normalize only the package metadata field, then run EPUBCheck again.

Matched

A manifest item is missing id or media-type.

The file exists, but content.opf does not give its file-list entry an internal label or confirmed file type.

Add the generated id or detected media type only when the packaged file makes the value unambiguous.

Matched

The same file is listed more than once in the manifest.

Some entries are byte-for-byte identical; others use different ids or settings and may still be referenced by the book.

Remove only identical copies or a proven unused equivalent entry. Conflicting entries need manual review.

Matched

MED_016 or RSC_005 points to package media:duration.

The package read-aloud total can be missing, malformed, or different from the refined durations declared for the SMIL items.

Recalculate only when every real, unique SMIL item has exactly one valid refined duration. Do not infer timing from MP3 files or incomplete metadata.

Metadata and OPF phrases to check

EPUB metadata checker: OPF metadata, unique-identifier, dcterms:modified, manifest fields, duplicate entries, media:duration, MED_016, and package field errors.

Where EPUB metadata errors appear

KDP, Kindle Previewer, EPUBCheck, Apple Books, Google Play Books, or another platform reports OPF metadata, identifier, modified date, manifest item, media:duration, duplicate entry, property, or media-type issues.

What it means

Metadata errors usually live in content.opf.

Common causes include a missing identifier target, draft identifiers, missing or malformed modified metadata, incomplete manifest items, duplicate entries, missing feature properties, wrong media types, stale package fields, or a package duration that does not match complete per-SMIL declarations.

Before you edit

Check the OPF package tag and metadata block together.

Do not edit visible title or author fields to fix an OPF identifier problem. The validator usually cares about id links, required metadata, and package wiring.

  1. 1Find the OPF file path from the EPUB package or report.
  2. 2Check the package unique-identifier value and whether a matching metadata element id exists.
  3. 3Check required fields such as language and modified date only in the OPF metadata block.
  4. 4Check whether each manifest item has an id, href, media-type, and any scripted, svg, mathml, or switch property required by its existing content.
  5. 5Compare duplicate manifest entries before removing anything; different ids can still be referenced from the spine, metadata, or content files.
  6. 6For MED_016 or package duration RSC_005, confirm every unique SMIL manifest item has exactly one valid media:duration that refines its id before changing the total.
  7. 7Repair only when one metadata or package value is clear and EPUBCheck passes again.
  8. 8Use the source tool or publisher metadata workflow for sales copy, categories, and listing fields.

Why KDP checks it

Why validators check EPUB metadata.

EPUB 3.3 package rules

The OPF file is the EPUB's map: metadata, file list, reading order, and navigation wiring. KDP and EPUBCheck use it to decide whether the book package is coherent.

EPUBCheck

EPUBCheck checks EPUB 2 and EPUB 3 files against the official rules and reports package, markup, link, and file-reference problems.

KDP eBook file formats

KDP supports EPUB files that meet Kindle Publishing Guidelines and recommends checking the file with Kindle Previewer before upload.

Repair example

When EPUB metadata can be repaired safely.

Before / after example

Before: unique-identifier points to bookid, but no metadata element has id=bookid. After: align it only when one real dc:identifier is clearly intended. Before: several identifiers compete; stop for manual review.

Ready to retry?

Scan the EPUB metadata and package fields.

Upload the EPUB so the report can inspect content.opf, identifier links, modified metadata, manifest item attributes, duplicate entries, media types, feature properties, media-overlay duration declarations, and package-level wiring.

Upload EPUB to scan

FAQ

Questions authors ask about EPUB metadata checks.

Is this an EPUB metadata editor?

This guide covers OPF structure and validation blockers. The separate EPUB metadata editor lets you change the title, author and language inside a file; neither workflow edits retailer listings, categories or keywords.

What file contains EPUB metadata?

The OPF package file, often content.opf, contains the metadata block, manifest, spine, and package fields.

Can EPUB Fixer repair OPF_030?

Only when one real dc:identifier is clearly the intended package identifier. If several identifiers compete, the report stops for manual review.

Can it repair a manifest item missing id or media-type?

Only when the existing item is unique and the packaged file provides one exact id or detected media type. If the file type or intended target is unclear, the report stops for manual review.

Can it remove duplicate OPF manifest items?

Only when the entries are identical, or when one equivalent entry is already used and the others are provably unused. Conflicting duplicate ids, hrefs, properties, or references remain manual.

Can it repair MED_016 or package media:duration?

Only when every real, unique SMIL manifest item already has exactly one valid refined media:duration. The package total can then be calculated from those declarations. Missing, duplicate, or malformed per-SMIL durations need manual review; the tool does not inspect MP3 length to guess timing.

Does changing KDP title or author fix OPF metadata errors?

Usually no. OPF validation errors are inside the EPUB package, not the KDP listing form.

Related EPUB error guides