EPUB FixerKDP upload error scanner

EPUB error guide

EPUBCheck errors: find the affected file and next step

Keep the exact EPUBCheck code, message, and path. Use them to separate missing resources, OPF or NCX wiring, ZIP packaging, and XHTML parse errors before you change the EPUB.

Scan EPUB structureSee an example report

Keep first

Save the complete error line.

The code, message, and file path together show what EPUBCheck found. A code by itself is not enough to choose a fix.

Find next

Locate the affected EPUB file.

RSC usually points to links, resources, or markup; OPF and NCX to package or navigation files; PKG to the ZIP or container; and MED to read-aloud media overlays.

Check before fixing

Not every error has a safe automatic fix.

Missing content, unclear anchors, reading order, and formatting choices need the source project or manual review.

Scan when the message does not name the affected path. The report shows affected paths and repair decisions, not manuscript text.

No signup before the scan report.Checks EPUB package paths, not manuscript text.Repair download only after EPUBCheck passes again.

Need fixed-layout, DRM, or source-file help? Check unsupported or review-first EPUB cases.

Match these report titles

  • EPUBCheck error code
  • RSC, OPF, NCX, or PKG validation message
  • EPUBCheck RSC OPF NCX PKG errors
  • RSC_005 error while parsing file
  • RSC_005 required element or attribute is missing
  • RSC_005 XML well-formedness, named entity, namespace, encoding, control character, DOCTYPE, occurrence, or IDREF error
  • EPUB XHTML parse error
  • HTML named entity is not valid in XML
  • XHTML namespace or XML encoding error
  • MED_011, MED_012, MED_013, MED_014, MED_016, MED_017, or MED_018 media overlay error
  • EPUBCheck structural blocker
  • EPUBCheck path, metadata, navigation, or package issue

Use this guide when

Your message matches "EPUBCheck error code" 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.

Error textAffected pathDecisionRepair, review, or stop

A useful report does not stop at the error name. It connects the message to an internal file and a next action.

Match the report title.

Look for "EPUBCheck error code" or the closest title above. Keep the original EPUBCheck, KDP, or Kindle Previewer wording if it differs.

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_005, RSC_007, RSC_012, OPF_030, NCX_001, PKG_006, MED_016, 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, resources, anchors, and XHTML parsing.

Start with the named XHTML or resource path. A missing file, missing anchor, duplicate id, named entity, namespace, or encoding error needs a different next step.

OPF / NCX / MED

Package metadata, navigation, and read-aloud wiring.

Open content.opf, toc.ncx, or the named SMIL file before changing visible content; repair only when every package relationship and target is unique.

PKG

ZIP wrapper and container problems.

Check mimetype order, compression, container.xml, and OPF rootfile paths before editing chapters or rebuilding the package.

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 error code, then find the affected path.

EPUBCheck can report many lines for one root problem. Keep the exact code and message, then group the output by family: RSC for links, resources, and markup; OPF and NCX for package or navigation wiring; PKG for ZIP or container problems; and MED for read-aloud media overlays.

Matched

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.

Matched

Can it be fixed automatically?

A checked repair is possible when the scan independently confirms one clear structural correction, including a package, manifest, metadata, navigation, path, anchor, media-type, media-overlay connection, duration total, ZIP, XHTML namespace, known named entity, or supported encoding fix.

Matched

What to check next

Copy the exact EPUBCheck code and message before editing.

Matched

What not to assume

It stops when the correct fix would require choosing missing content, chapter order, note targets, narration timing, read-aloud order, 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.

Matched

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.

Matched

RSC_005 says an XHTML file could not be parsed.

The cause may be a duplicate id, an HTML named entity, a missing XHTML namespace, or a wrong XML encoding declaration.

Keep the file path and full parser message. Duplicate ids need manual review; deterministic encoding, namespace, entity, or matching language-label problems can be reported separately by the scan.

Matched

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.

Matched

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.

Matched

MED errors for read-aloud media overlays.

MED_011 through MED_018 can involve page-to-SMIL connections, audio or text fragments, and package duration metadata.

Use the report to check the named OPF, SMIL, XHTML or SVG path. Automatic repair is allowed only when the existing files prove one connection or fragment value without changing narration timing or reading order.

EPUBCheck RSC, OPF, NCX, PKG, NAV, and MED messages to check

EPUBCheck errors: RSC, OPF, NCX, PKG, NAV, MED, and XHTML parse messages that point to package, metadata, navigation, link, anchor, manifest, media overlay, markup, or ZIP 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, XHTML parse errors, wrong OPF identifiers, missing manifest items, wrong media types, disconnected navigation, invalid NCX wiring, broken SMIL connections or duration metadata, 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.

  1. 1Copy the exact EPUBCheck code and message before editing.
  2. 2Find the affected internal path, such as content.opf, nav.xhtml, toc.ncx, a chapter XHTML file, CSS file, image path, or ZIP entry.
  3. 3Group repeated messages by source file and target path instead of fixing every line separately.
  4. 4Identify whether the issue is package metadata, manifest, spine, navigation, link, anchor, media type, container, or ZIP wrapper.
  5. 5Use checked repair only when one structural change is clear and the repaired EPUB passes EPUBCheck again.
  6. 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

A checked repair is possible when the scan independently confirms one clear structural correction, including a package, manifest, metadata, navigation, path, anchor, media-type, media-overlay connection, duration total, ZIP, XHTML namespace, known named entity, or supported encoding fix.

When you need manual review

It stops when the correct fix would require choosing missing content, chapter order, note targets, narration timing, read-aloud order, 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 scan

FAQ

Questions authors ask about EPUBCheck error codes.

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.

Does RSC_005 always mean duplicate ID?

No. The full message can identify a duplicate id, missing required element or attribute, illegal namespace or element, malformed XML, named entity, encoding, forbidden control character, DOCTYPE, occurrence, or unresolved IDREF problem. Keep the complete message because the code alone does not choose the next step.

Can EPUB Fixer repair an XHTML parse error?

Only when the scan finds a deterministic change such as a missing or wrong XHTML namespace, a supported encoding conversion, a known HTML named entity, or one missing matching language label. Duplicate ids and malformed document structure remain manual.

Can EPUB Fixer repair MED media-overlay errors?

Only in narrow cases where the OPF, SMIL, XHTML or SVG files prove one page connection, one case or URL-encoding fragment correction, one empty audio fragment removal, or one package duration total. It does not guess narration timing, text highlights, audio order, or which competing SMIL file is correct.

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.

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