Match the report title.
Look for "EPUB metadata check" or the closest title above. Keep the original EPUBCheck, KDP, or Kindle Previewer wording if it differs.
EPUB error guide
EPUB metadata checker
Use this when you need to check EPUB metadata structure in content.opf, including unique identifiers, language, modified date, manifest links, and package fields that can block validation.
Scan when the message does not name the affected path. The report shows affected paths and repair decisions, not manuscript text.
Fixed-layout, DRM, or source-workflow issue? Check unsupported or review-first EPUB cases.
Match these report titles
- EPUB metadata check
- OPF metadata error
- Unique identifier or dc:identifier problem
- EPUB package metadata blocker
Use this guide when
Your message matches "EPUB metadata check" or one of the report titles above.
Upload if
You have the exported reflowable .epub and need the affected path, file, field, or repair decision before editing.
Handle outside this tool
Use the source tool or publishing workflow for DOCX, PDF, KPF, KCB, fixed-layout, comics, image-first books, DRM, visual design, or KDP listing and approval problems.
Read the scan report
Decide if this report item matches.
Use the report label, affected file, and repair decision together. A matching title alone is not enough if the file path or EPUB structure points to a different problem.
Check the affected file first.
Use the Affected area, Source file, Target file, or Problem type rows before editing OPF, nav, XHTML, CSS, or image paths.
Follow the repair decision.
Repairable means one clear structural change. Needs review or Not supported means use the named file, source project, or platform step.
Keep with your repair note.
Copy these fields from the report instead of rebuilding the fix from memory.
Source file
Target path or field
Original error
Repair decision
Next step
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, dc:language, dcterms:modified, manifest item, or package field.
Validator signal
OPF_030, OPF_048, OPF_049, language, modified date, manifest, 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.
Some OPF metadata problems are simple wiring fixes; others require knowing 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.
Required fields
Use this when language or modified date is missing.
Add or normalize only values that are clear from the book metadata and EPUB rules.
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 is missing or wired incorrectly.
A clear unique-identifier, language, modified date, manifest, or media-type mismatch can often be checked safely.
Manual fit
Several identifiers or metadata values could be right.
The report can name the candidates, but a person should choose the real book identifier or language.
Not this tool
You want to edit sales metadata.
Title, subtitle, author bio, categories, keywords, pricing, synopsis, and retailer listing metadata belong in the publishing platform or source workflow.
Start here
Check OPF metadata structure, not marketing metadata.
This is not a metadata editor for polishing title, author, or synopsis. It checks whether content.opf metadata and package fields line up well enough for KDP, Kindle Previewer, and EPUBCheck validation.
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.
Can it be fixed automatically?
EPUB Fixer can help when the correct OPF metadata change is clear and can be checked again, such as one missing package link, one required language value, one modified date normalization, or one media-type correction.
What to check next
Find the OPF file path from the EPUB package or report.
What not to assume
It does not choose between competing ISBN/UUID/retailer identifiers, rewrite title or author metadata for sales pages, pick categories, create descriptions, or decide publishing platform listing fields.
Common situations
Common EPUB metadata checker cases.
Start with the OPF field that the validator names.
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.
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.
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.
Metadata and OPF phrases this page can help with
EPUB metadata checker: OPF metadata, unique-identifier, dc:identifier, language, dcterms:modified, manifest, media-type, and package field validation errors.
Where EPUB metadata errors appear
KDP, Kindle Previewer, EPUBCheck, Apple Books, Google Play Books, or another platform reports OPF metadata, identifier, language, modified date, manifest, or media-type issues.
What it means
Metadata errors usually live in content.opf.
EPUB metadata lives in the OPF package document. Validators check whether required fields exist and whether package fields point to real metadata entries.
Common causes include package unique-identifier pointing to a missing id, multiple identifiers from draft exports, missing language metadata, duplicate or malformed dcterms:modified values, wrong manifest media types, and source tools leaving stale package fields.
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.
- 1Find the OPF file path from the EPUB package or report.
- 2Check the package unique-identifier value and whether a matching metadata element id exists.
- 3Check required fields such as language and modified date only in the OPF metadata block.
- 4Compare manifest items and media types when metadata errors involve package inventory.
- 5Repair only when one metadata or package value is clear and EPUBCheck passes again.
- 6Use 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.
Can this be fixed safely?
When EPUB metadata can be repaired safely.
When automatic repair is safe
EPUB Fixer can help when the correct OPF metadata change is clear and can be checked again, such as one missing package link, one required language value, one modified date normalization, or one media-type correction.
When you need manual review
It does not choose between competing ISBN/UUID/retailer identifiers, rewrite title or author metadata for sales pages, pick categories, create descriptions, or decide publishing platform listing fields.
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, required metadata fields, identifier links, manifest references, media types, and package-level wiring.
Upload EPUB to scanFAQ
Questions authors ask about EPUB metadata checks.
Is this an EPUB metadata editor?
No. It checks OPF metadata structure and validation blockers. It does not edit sales metadata, categories, keywords, or descriptions.
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.
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.