EPUB error guide

EPUBCheck RSC-005 duplicate ID

What duplicate ID and RSC_005 EPUB parsing errors mean, and why many require careful review.

Error text

RSC_005: Error while parsing file. Duplicate ID.

When you usually see it

EPUBCheck cannot parse an XHTML file cleanly because the same id appears more than once, or markup is malformed.

Plain English

What it means inside the EPUB.

IDs are supposed to be unique within a document. Duplicate IDs can break links, footnotes, TOC anchors, and reading system behavior.

Duplicate IDs often appear after copy-paste editing, automatic export bugs, or manual XHTML edits.

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.

Find the XHTML file named in the validator message and locate repeated id values or malformed markup.
Check whether any nav, NCX, footnote, or internal link points to the duplicated id.
Avoid automatic changes when changing an id would affect reading order, semantic footnotes, or author-intended links.

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.

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.

Repairability

Can EPUB Fixer repair it?

Safe repair condition

V1A treats this as a whitelist repair area. Simple duplicate attributes or clearly isolated duplicate IDs may be repairable after revalidation.

When it stops at diagnosis

The tool should not rewrite complex XHTML structure, MathML-heavy content, semantic footnotes, or cases where changing an id would break author-intended links.

Before / after example

Before: two headings use id="subhead-1". After: a safe repair is only possible if references can be updated without changing reading order or meaning.

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