Have the exact EPUBCheck code?
Open the matching RSC, OPF, or PKG guide first. It tells you which file path, anchor, metadata field, or package rule to inspect before changing the EPUB.
KDP upload errors, Kindle Previewer messages, and EPUBCheck codes explained.
Got a KDP upload error, a Kindle Previewer warning, or an EPUBCheck code? Save the exact wording first. Match it here before you edit the EPUB, then decide whether you need a guide or a scan that names the affected file path.
- 1Match the messageUse the exact EPUBCheck code, KDP sentence, or Kindle Previewer wording you already have.
- 2Open the guideCheck the usual path, anchor, OPF, navigation, or ZIP packaging cause.
- 3Scan if it is vagueUpload the EPUB when the error does not name the affected file, anchor, OPF field, or ZIP packaging rule.
Find the right guide
Start with the exact words on screen.
Open the matching guide when your KDP, Kindle Previewer, or EPUBCheck message contains one of these phrases.
Paste error triage
Paste the KDP, Kindle Previewer, or EPUBCheck wording.
This only matches the wording. The scanner does not inspect your EPUB until you upload the file.
Paste the exact error line to see the likely guide, what part of the EPUB it affects, and whether you still need to upload the file.
- RSC_007: Referenced resource could not be found in the EPUBRSC_007 missing resource
- RSC_012: Fragment identifier is not definedRSC_012 broken anchor
- Broken internal links, missing files, or missing anchorsBroken links and anchors
- EPUB table of contents, nav.xhtml, or toc.ncx is missingTOC and navigation
- OPF file not found in the EPUBOPF_002 package path
- OPF_030: The unique-identifier was not foundOPF_030 metadata
- RSC_008: Referenced resource is not declared in the OPF manifestOPF_003 / RSC_008 manifest item
- RSC_011: Referenced resource is not a spine itemTOC target not in spine
- NCX_001: NCX identifier does not match OPF unique identifierdtb:uid mismatch
- NCX_002: NCX is not linked from the spine toc attributeNCX spine toc wiring
- Manifest media-type does not match the file extensionOPF_029 media-type mismatch
- OPF_010: Error resolving referenceOPF path resolution
- PKG_006: Mimetype file entry is missing or is not the first filePKG_006 ZIP packaging
- PKG_007: Mimetype file contents are invalid or compressedMimetype compressed EPUB
- PKG_010: Filename contains spaces or URI escaping is necessaryPath case / URL encoding
- Kindle Previewer reports EPUB validation errorsKindle Previewer report
Choose your path
Pick the guide based on what you have.
Some people arrive with an EPUBCheck code. Others only have a KDP upload message. Either way, the next step is to find the affected path before guessing at a fix.
Only have a KDP or Kindle Previewer message?
Use the message matcher first. If the wording is vague, scan the EPUB so the report can point to the affected path instead of making you re-export blindly.
Not sure if it can be fixed safely?
Upload the actual EPUB to separate automatic fixes, manual checks, and problems that are outside EPUB structure repair.
Find the error you see
Broken references and anchors
Start here when EPUBCheck or KDP points to a missing image, stylesheet, chapter file, broken link target, or duplicate XHTML id.
- EPUB broken links and missing anchors
Use this when KDP or EPUBCheck says an internal link, image, stylesheet, or anchor is broken. Separate missing file paths from missing #id targets before you retry the EPUB.
- Referenced resource could not be found in the EPUB
Use this when KDP, Kindle Previewer, or EPUBCheck says a referenced resource could not be found, a reference cannot be resolved, or a path needs URI escaping. Match the exact internal path before you rename files or re-export the book.
- RSC_007 referenced resource could not be found
Use this when you already have the exact RSC_007 line. Follow the source file and missing target path before you change nav.xhtml, content.opf, chapters, images, or CSS.
- RSC_012 fragment identifier is not defined
Use this when the target file exists but the link destination after # is missing. Check the XHTML file and anchor id before you edit TOC, footnotes, or chapter links.
- EPUBCheck RSC-005 duplicate ID
Use this when EPUBCheck reports a duplicate id in XHTML. Check every repeated id and every link that targets it before you rename or remove anything.
Find the error you see
Package and metadata errors
Start here when the EPUB package cannot be opened cleanly, container.xml points to the wrong OPF file, metadata identifiers do not line up, or the mimetype file was zipped in the wrong place.
- OPF_030 unique-identifier was not found
Use this when the OPF package points to a missing identifier id. Match the package unique-identifier to a real dc:identifier before another KDP upload.
- OPF_029 manifest media-type mismatch
Use this when content.opf declares the wrong media type for a real packaged file. Match the manifest entry to the actual file before you retry the EPUB.
- OPF_003 item is not declared in the OPF manifest
Use this when a file exists in the EPUB but content.opf does not declare it, or when EPUBCheck says a referenced resource is not declared in the OPF manifest. Check whether the file is actually used before you add a manifest item.
- OPF_048 package is missing unique-identifier
Use this when the OPF package tag has no unique-identifier. Check whether one real dc:identifier should identify the book before you edit the metadata.
- OPF_049 item id was not found in the manifest
Use this when an OPF reference names a manifest id that does not exist. Find where the missing id is used before you change spine or navigation wiring.
- Mimetype compressed EPUB and invalid mimetype contents
Use this when the EPUB mimetype file contents are wrong or the file is compressed. Check the ZIP wrapper before you touch chapters, OPF, or navigation files.
- OPF rootfile path mismatch
Use this when container.xml points to an OPF path the EPUB does not contain, or when the rootfile path is wrong. Find the real package file before you change the rootfile path.
- container.xml missing in EPUB
Use this when META-INF/container.xml is missing or not usable. Confirm the real OPF package path before you rebuild the EPUB container map.
- PKG_006 mimetype file entry is missing or not first
Use this when manual zipping or repackaging broke the EPUB container. Check whether the root-level mimetype file is missing, compressed, or not first in the ZIP.
What the report will tell you
Use the report label to decide the next action.
Either fix it automatically, review the affected file by hand, or stop because the problem is not an EPUB structure issue.
- Automatic fixThe report found one clear package, metadata, reference, or container change and checks the repaired EPUB again before download.
- Manual checkOpen the affected file because the right change depends on the book's intended content or reading order.
- Not supportedUse the source tool, EPUB editor, or KDP workflow because the issue is outside EPUB structure repair.
If this is not a structure error
Use the source tool or KDP workflow instead.
- Have a DOCX, PDF, KPF, KCB, or ZIP archive? Export a real .epub before using this scanner.
- Have a fixed-layout, comic, picture book, manga, or image-first EPUB? Use the source design tool or a specialist workflow.
- Need DRM removal, cover design, typography, book formatting, or KDP account help? That work happens outside the EPUB structure scan.