EPUBCheck RSC-007, RSC-008 and RSC-012 Errors Explained: How to Fix Broken Links in an EPUB

RSC-007 means a link or reference points to a file that is not in the EPUB, RSC-008 means the file is in the EPUB but is not listed in the package manifest, and RSC-012 means the link’s #fragment does not match any id in the target file. EPUBCheck classes all three as errors, and all three are broken references, and the fix is almost always in a path, a file name’s capitalization, a manifest entry or an id. ProofSlip checks an EPUB’s package, navigation and broken links on your PC and explains in plain language what to fix, so you can find these before a retailer’s upload does.

The message texts below are quoted from EPUBCheck’s own message bundle, and the rules come from the EPUB 3.3 specification.

Check an EPUB for broken links and package problems before you upload.

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What do the three errors say?

Code	EPUBCheck message	In plain terms
RSC-007	Referenced resource ”…” could not be found in the EPUB.	The link points to a file that is not there
RSC-008	Referenced resource ”…” is not declared in the OPF manifest.	The file is there, but the package does not list it
RSC-012	Fragment identifier is not defined.	The file is there, but the #part after it is not

EPUBCheck reports each one with the file and line where the bad reference sits. Start there: the problem is in the file doing the linking, not always in the file being linked to.

What causes RSC-007, resource could not be found?

The reference names a path that does not exist inside the EPUB. The common causes:

1. A typo or a renamed file. You renamed chapter-03.xhtml to chapter-3.xhtml, and the table of contents still points at the old name.
2. A wrong relative path. Paths are resolved from the file that contains the link. A chapter in a Text folder that links to Images/map.jpg is looking for Text/Images/map.jpg. It needs ../Images/map.jpg.
3. Capitalization. EPUB 3.3 says file paths and file names are case sensitive. A link to cover.jpg does not find Cover.jpg.
4. A file that was never added. A font or image referenced in the CSS was left out when the book was built.

The capitalization case catches many Windows users, because Windows file systems usually treat Cover.jpg and cover.jpg as the same file. If you edit an unzipped book in a folder and test it in a browser, the wrong-case link works. Inside the EPUB container it does not, and a reading system that follows the specification will not find it.

Fix: open the file named in the error, find the reference, and correct the path or name so it matches the file exactly, letter case included.

What causes RSC-008, not declared in the OPF manifest?

Every EPUB has a package document, usually named content.opf, with a manifest that lists the book’s files. EPUB 3.3 says the manifest must list all publication resources. RSC-008 means a file was referenced and does exist, but has no item in that list.

This usually happens when a file is added to the folder by hand, or copied in from another book, and the manifest is not updated. It is easy to miss when files are added by hand or by a script.

Fix: add an item to the manifest with a unique id, the href relative to the package document, and the correct media-type:

<manifest>
  <item id="map" href="Images/map.jpg" media-type="image/jpeg"/>
</manifest>

Check the href against the actual path and capitalization. If the href is wrong, you trade RSC-008 for a different missing-file error.

What causes RSC-012, fragment identifier is not defined?

A link can point to a place inside a file: notes.xhtml#n12 means the element with id="n12" in notes.xhtml. RSC-012 means the file exists but no element in it has that id.

Common causes:

• Split chapters. A long file was split in two, and the table of contents or a cross-reference still points at chapter1.xhtml#section4, which now lives in chapter1b.xhtml.
• Renamed or deleted ids. A style clean-up removed id attributes that footnotes or the index relied on.
• Mismatched ids. #Note12 and id="note12" differ in case, and ids are compared exactly.
• Footnote round trips. The note links back to its reference mark, but the reference mark never got an id.

Fix: either add the missing id to the right element in the target file or correct the link to an id that exists. In a footnote-heavy book, check both directions of each note.

Which related errors often appear alongside them?

Code	EPUBCheck message
RSC-011	Found a reference to a resource that is not a spine item.
RSC-020	”…” is not a valid URL (…)
RSC-026	URL ”…” leaks outside the container
RSC-033	Relative URL strings must not have a query component

RSC-011 means a hyperlink goes to a content file that is in the manifest but not in the reading order, the spine. Either add the file to the spine or link somewhere else. RSC-026 usually means a path climbs out of the book with too many ../ segments. RSC-020 can come from characters that are not valid in a link, such as a raw space. EPUB 3.3 says file names should not contain spaces, for compatibility with older reading systems, so renaming such files and their links avoids the issue.

Get a plain-language list of what to fix in your EPUB, Word file or print PDF.

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How do you stop broken links coming back?

• Rename through your editor, not in File Explorer, so the tool updates links and the manifest together.
• Use one naming style, all lowercase with hyphens, so capitalization never differs between a file and its links.
• Avoid two names that differ only in case. EPUB 3.3 requires file names in the same folder to stay unique after case folding, so Map.jpg and map.jpg cannot sit side by side.
• Re-check after every split or merge of chapters, since that is when fragments move.
• Validate the final file, the one you upload, not a working copy.

How does ProofSlip help?

ProofSlip is a Windows app that checks print PDFs, EPUBs and Word manuscripts on your PC and says, in plain language, what to fix before you send them. For an EPUB it checks the package and navigation, broken links, missing alt text, the cover and accessibility details. Its book details check verifies ISBN check digits and compares the title and ISBN with your EPUB.

You can drop a whole job, such as the EPUB, the Word manuscript and the print PDFs, on the window and export every report at once. There is no account and no upload: files never leave your PC and are never changed.

ProofSlip is not a replacement for the validator your retailer runs. Our guide to checking an EPUB before uploading to KDP, Apple Books and Kobo covers what each retailer requires. If the same book is going to print, see checking a KDP paperback PDF before upload.

Frequently asked questions

Will a store reject an EPUB with RSC-007?

EPUBCheck reports RSC-007 as an error, and retailers that validate uploads with EPUBCheck may reject a file that has errors. Fix every error before you upload.

Why does the link work in my editor but fail in EPUBCheck?

Usually capitalization or a path that only resolves on your PC. Windows tends to ignore case; the EPUB container does not.

Can I just delete the broken link?

Yes, if the target is not needed. For a missing image or font, deleting the reference changes how the book looks, so add the file instead if it belongs.

Is RSC-012 serious if the file still opens?

A broken fragment usually lands the reader at the top of the file instead of the right spot, or nowhere. It is still reported as an error, so fix it.

Try ProofSlip

ProofSlip is a one-time purchase with a free trial in the Microsoft Store; the listing shows the current price and system requirements. Run it on your final EPUB and fix the link findings before you upload. More detail is on the ProofSlip product page.

Find broken links, missing alt text and package problems before your retailer does.

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Automata Labs is not affiliated with the W3C or the EPUBCheck project.

Last updated 23 October 2026. Published by Automata Labs, a software company in Canada.