Match the report title.
Look for "EPUBCheck error" or the closest title above. Keep the original EPUBCheck, KDP, or Kindle Previewer wording if it differs.
EPUB error guide
EPUBCheck errors
Use this when EPUBCheck reports RSC, OPF, NCX, or PKG errors and you need to know which EPUB file, path, anchor, metadata field, manifest item, or ZIP rule is blocking 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
- EPUBCheck error
- RSC, OPF, NCX, or PKG validation message
- EPUBCheck structural blocker
- EPUBCheck path, metadata, navigation, or package issue
Use this guide when
Your message matches "EPUBCheck error" 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 an EPUBCheck-focused report should show.
A useful report should preserve the original EPUBCheck wording while adding a practical file-level decision.
Original code
RSC_007, RSC_012, OPF_030, OPF_003, NCX_001, PKG_006, or another EPUBCheck family.
Affected file
The OPF, nav.xhtml, toc.ncx, chapter XHTML, CSS, image, or ZIP entry related to the message.
Root blocker
The first issue to inspect before fixing secondary messages.
Decision
Repairable, manual review, or unsupported.
Recheck
Run EPUBCheck again after any structural repair before retrying KDP or another platform.
The report should reduce the EPUBCheck output into a repair order instead of turning every line into a separate task.
2. Next step
Use the EPUBCheck family to choose the next step.
The code family usually tells you which EPUB layer to inspect first.
RSC
Links, anchors, resources, and XHTML references.
Start with the source file and target path or fragment. Missing files and missing anchors require different fixes.
OPF / NCX
Package metadata, manifest, spine, and navigation wiring.
Open content.opf or toc.ncx before changing visible chapter content.
PKG
ZIP wrapper and container problems.
Check mimetype order, compression, container.xml, and OPF rootfile paths before editing chapters.
3. Concrete path example
EPUBCheck output often needs grouping.
Fixing the first package problem can remove several secondary lines.
EPUBCheck: OPF_030: unique-identifier was not found RSC_007: referenced resource could not be found RSC_012: fragment identifier is not defined Report: Primary blocker: content.opf metadata identifier mismatch Secondary blocker: nav.xhtml contains stale chapter and anchor links Decision: repair OPF only if one dc:identifier is clear; review nav links separately
Do not assume the first line printed by EPUBCheck is the only issue. Use the affected paths to decide repair order.
Quick decision
Decide whether the EPUBCheck error is structural or editorial.
EPUBCheck validates package rules. Some problems are safe package repairs; others point to missing content or reader-destination decisions.
Good fit
The error names package, metadata, navigation, link, anchor, manifest, or ZIP structure.
These are the messages EPUB Fixer is designed to locate and classify.
Manual fit
The error points to missing content or ambiguous links.
The report can still hand you the affected path, but the final choice may belong in the source project or EPUB editor.
Not this tool
The problem is visual formatting, conversion, or platform policy.
Use the source formatter, conversion tool, or platform workflow rather than treating it as an EPUBCheck repair.
Start here
Start from the EPUBCheck message, then find the affected path.
EPUBCheck can report many lines for one root problem. Keep the exact code and message, then use the report to connect it to the OPF, nav, NCX, XHTML, CSS, image, anchor, manifest, or ZIP entry that needs attention.
What it means
EPUBCheck checks whether the EPUB package follows EPUB rules. The code points to a category, but the useful fix depends on the affected internal file and path.
Can it be fixed automatically?
EPUB Fixer can help when the report finds one clear package, manifest, metadata, navigation, path, anchor, media-type, or ZIP correction that can be checked with EPUBCheck again.
What to check next
Copy the exact EPUBCheck code and message before editing.
What not to assume
It stops when the correct fix would require choosing missing content, chapter order, note targets, visible layout, source formatting, conversion output, platform policy, or anything outside the EPUB structure.
Common situations
Common EPUBCheck error searches.
Start from the code family if you have one. If you only have a long report, scan the EPUB and use the grouped result.
RSC errors for missing resources or anchors.
These usually involve XHTML, CSS, nav.xhtml, toc.ncx, images, chapter paths, or fragments after #.
Check source and target paths separately before renaming files or adding anchors.
OPF errors for metadata, manifest, or spine.
These usually involve content.opf, identifiers, manifest entries, media types, or reading order references.
Open content.opf and inspect the specific field before changing visible book content.
PKG errors for ZIP or container packaging.
These usually involve mimetype, compression, container.xml, or the OPF rootfile path.
Fix package wrapper issues first because they can hide deeper validation errors.
EPUBCheck messages this page can help with
EPUBCheck errors: RSC, OPF, NCX, and PKG messages that point to EPUB package, metadata, navigation, link, anchor, manifest, or ZIP validation problems.
Where EPUBCheck errors usually appear
EPUBCheck reports one or more errors before KDP, Kindle Previewer, Apple Books, Google Play Books, or another publishing workflow accepts the EPUB.
What it means
One EPUBCheck code can hide several different file-level causes.
EPUBCheck checks whether the EPUB package follows EPUB rules. The code points to a category, but the useful fix depends on the affected internal file and path.
Common causes include missing resources, missing anchors, wrong OPF metadata identifiers, missing manifest items, wrong media types, disconnected navigation, invalid NCX wiring, bad container.xml paths, and incorrectly packaged ZIP wrappers.
Before you edit
Group the EPUBCheck output before editing.
Do not fix errors one line at a time until you know whether several messages share the same missing file, manifest entry, metadata id, navigation file, anchor, or ZIP wrapper problem.
- 1Copy the exact EPUBCheck code and message before editing.
- 2Find the affected internal path, such as content.opf, nav.xhtml, toc.ncx, a chapter XHTML file, CSS file, image path, or ZIP entry.
- 3Group repeated messages by source file and target path instead of fixing every line separately.
- 4Identify whether the issue is package metadata, manifest, spine, navigation, link, anchor, media type, container, or ZIP wrapper.
- 5Use checked repair only when one structural change is clear and the repaired EPUB passes EPUBCheck again.
- 6Return to the source tool or EPUB editor when the report says manual review.
Why KDP checks it
Why EPUBCheck reports these problems.
EPUBCheck
EPUBCheck checks EPUB 2 and EPUB 3 files against the official rules and reports package, markup, link, and file-reference problems.
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.
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 an EPUBCheck error can be repaired safely.
When automatic repair is safe
EPUB Fixer can help when the report finds one clear package, manifest, metadata, navigation, path, anchor, media-type, or ZIP correction that can be checked with EPUBCheck again.
When you need manual review
It stops when the correct fix would require choosing missing content, chapter order, note targets, visible layout, source formatting, conversion output, platform policy, or anything outside the EPUB structure.
Before / after example
Before: EPUBCheck reports OPF_030 because package unique-identifier points to a missing metadata id. After: align it only when one real dc:identifier is clear and EPUBCheck passes again. Before: RSC_012 points to a missing footnote anchor; review the intended note target manually.
Ready to retry?
Scan the EPUB behind the EPUBCheck output.
Upload the same EPUB that produced the EPUBCheck output. The report can group related issues and show whether the next step is checked repair, manual review, or unsupported.
Upload EPUB to scanFAQ
Questions authors ask about EPUBCheck errors.
What is the fastest way to understand EPUBCheck errors?
Keep the original code, then find the affected EPUB file and path. The code family tells you the area, but the path tells you what to inspect.
Can EPUB Fixer repair every EPUBCheck error?
No. It can only repair clear structural issues. Missing content, ambiguous anchors, chapter order, source formatting, and visual layout need manual review.
Should I fix EPUBCheck errors in order?
Not always. Several lines can come from one root package problem. Group them by source file and target path first.
Can I use this before KDP upload?
Yes, if you already have a reflowable EPUB. Scan the EPUB output before another KDP or Kindle Previewer retry.