EPUB Error: Duplicate Item in OPF Manifest
What causes this error?
Every file in an EPUB must be declared exactly once in the OPF manifest. Each manifest item must have a unique id attribute and a unique href value — two items cannot point to the same file, and two items cannot share the same id. This error fires when the same file appears twice in the manifest under different ids, or when the same id is reused across two different manifest items. It most often occurs during manual OPF editing when an author adds a file that was already registered, or when two EPUB files are merged and their manifest sections are concatenated without checking for overlaps. It also appears in files generated by certain export tools that produce one entry for the internal package reference and a second for the file path.
How to fix it
- Open content.opf and search for the href value named in the error (e.g.,
images/cover.jpg). Locate both manifest items that reference the same file. - Determine which item is the correct one — check which id is referenced in the spine, the navigation document, or anywhere else in the file. The referenced entry should stay; the unreferenced duplicate should be removed.
- If the duplicate items have different ids and both are referenced elsewhere, consolidate to one: update all other references to use the surviving id, then remove the duplicate manifest item.
- After removing the duplicate manifest entry, confirm the spine contains no orphaned
<itemref>pointing to the deleted id — remove those too if present. - Re-validate with EPUBCheck to confirm no duplicate href or id values remain in the manifest.
Common questions
Is a duplicate manifest item the same as a duplicate id attribute in content?
No — a duplicate manifest item means the same file is listed twice inside the OPF manifest section. A duplicate id attribute (a separate EPUBCheck error) means the same id value is used on two HTML elements inside a chapter XHTML file. The manifest item error is a package-structure problem; the id duplication error is a content-file problem.
Can two manifest items have the same id but different hrefs?
No. Both the id and the href must be unique within the manifest. Duplicate ids are an immediate XML validity failure because id attributes must be unique within any XML document. Duplicate hrefs fail the EPUB specification separately, since each physical file can only have one canonical manifest entry.
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