EPUB 3.3 package document
The package document defines the metadata, manifest, spine, and navigation wiring that validators inspect before a reading system can process the book reliably.
EPUB error guide
OPF-030 unique identifier not found
How OPF_030 unique-identifier errors happen and how EPUB Fixer checks OPF metadata safely.
Error text
OPF_030: The unique-identifier was not found.
When you usually see it
EPUBCheck rejects the OPF package because the package unique-identifier points to an ID that is not declared in metadata.
Plain English
What it means inside the EPUB.
The OPF says 'this is the book identifier', but the identifier it names does not exist.
The package tag may reference unique-identifier="BookId" while the metadata contains a dc:identifier with a different id, or no id at all.
User checklist
What to inspect before another upload.
These checks keep the repair decision tied to the EPUB package instead of guessing from a generic error code.
- Open the OPF package file and find the package unique-identifier value.
- Check whether the metadata section contains a dc:identifier with the same id value.
- Do not choose between conflicting ISBN, UUID, or platform identifiers without knowing the intended publishing identifier.
Standards context
Why this error matters to validators.
EPUBCheck
EPUBCheck evaluates EPUB 2 and EPUB 3 publications against official EPUB specifications and reports structure, package, markup, and reference problems.
Repairability
Can EPUB Fixer repair it?
Safe repair condition
This is often repairable by aligning the package unique-identifier with an existing dc:identifier, or by adding a deterministic identifier when the metadata is otherwise clear.
When it stops at diagnosis
The tool should not choose between conflicting ISBN, UUID, or channel identifiers when the intended publishing identifier is unclear.
Before / after example
Before: package unique-identifier="uid" but no dc:identifier id="uid" exists. After: the package and dc:identifier point to the same metadata entry.
Next step
Scan the actual file before editing by hand.
The same error code can come from different files and different causes. Uploading the EPUB lets the report show the affected path and whether the fix is deterministic.
Upload EPUB to scan