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.
Match a KDP, Kindle Previewer, or EPUBCheck error
Paste the exact line from KDP, Kindle Previewer, EPUBCheck, Apple Books, or a distributor. Open a guide when the message names the path; scan the EPUB when it does not.
Error text matcher
Paste the exact error line.
Check whether this looks like your EPUB error. Upload only when you need the exact file path and repair decision.
Paste one KDP, Kindle Previewer, or EPUBCheck error line.
Waiting for error text
- Likely guide
- The closest EPUBCheck, KDP, or Kindle Previewer guide.
- Affected area
- Path, anchor, OPF field, navigation, or ZIP packaging clue.
- When to upload
- Upload when you need the report to name the real EPUB path and next step.
- 1Match the messageUse the EPUBCheck code, KDP sentence, store rejection line, or Kindle Previewer wording already on screen.
- 2Open the guideCheck the likely path, anchor, OPF, navigation, or ZIP packaging cause.
- 3Scan if it is vagueUpload the EPUB when the message does not name the affected file, anchor, OPF field, or ZIP packaging rule.
Find the right guide
Common matching phrases.
Open the guide when your error contains one of these phrases. Use the paste matcher above when the wording is close but not exact.
- Free EPUB validator, online EPUB checker, validate EPUB, or check EPUB for errorsEPUB validator
- EPUB repair, repair EPUB, fix EPUB online, or checked EPUB structure repairChecked repair
- KDP ebook formatting error, upload failed, or Kindle Previewer validation problemKDP upload failed
- EPUB opens locally but fails KDP, Kindle Previewer, or EPUBCheckReader vs validator
- EPUB cover not showing, Kindle cover missing, or OPF cover-image problemEPUB cover
- EPUB 3 cover image is missing the cover-image propertyCover-image property
- DOCX to EPUB export, Word to EPUB output, or exported EPUB failed KDPAfter export check
- EPUBCheck errors, EPUBCheck online, or RSC / OPF / PKG validation messagesEPUBCheck error codes
- Invalid EPUB file, corrupt EPUB, damaged EPUB, or not a valid EPUBInvalid EPUB
- Kindle Previewer failed, conversion failed, or enhanced typesetting failedPreviewer conversion
- EPUB metadata checker, OPF metadata error, or unique identifier problemMetadata checker
- E20006: More than one title defined in OPF metadataDuplicate OPF title
- Apple Books or Google Play rejected EPUBStore rejection
- Draft2Digital, Smashwords, Kobo, Barnes & Noble Press, or IngramSpark rejected EPUBDistributor rejection
- RSC_005: Duplicate ID in an XHTML fileRSC_005 duplicate id
- 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
- EPUB navigation document or nav.xhtml is missingMissing nav document
- nav.xhtml is not declared in the OPF manifest or is missing properties navnav.xhtml OPF wiring
- OPF file not found in the EPUBOPF_002 package path
- RSC_003: No rootfile tag was found in container.xmlRSC_003 rootfile
- OPF_019: Spine tag was not found in the OPF fileOPF_019 spine
- OPF_030: The unique-identifier was not foundOPF_030 metadata
- dcterms:modified metadata is missing, duplicated, or malformeddcterms:modified 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
- PKG_021: Corrupted image file encounteredPKG_021 image
- PKG_022: Wrong file extension for imagePKG_022 image extension
- 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 compressedPKG_007 mimetype
- PKG_010: Filename contains spaces or URI escaping is necessaryPath case / URL encoding
- Kindle Previewer reports EPUB validation errorsKindle Previewer report
- Kindle conversion or enhanced typesetting failedPreviewer conversion failure
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.
Guide shortcuts
Jump to the error family.
Use these shortcuts when the paste matcher does not give you one clear guide.
Find the error you see
High-volume EPUB search entries
Start here if you searched broadly for EPUB validation or KDP upload failure and still have an exported EPUB file to scan before another retry.
- Free EPUB validator for KDP upload errors
Use this as a free online EPUB validator and checker when you need to check a reflowable EPUB for KDP upload, Kindle Previewer, EPUBCheck, package, metadata, navigation, link, anchor, or ZIP errors before another publishing retry.
- KDP EPUB upload failed and formatting errors
Use this when KDP upload fails or Kindle Previewer says your EPUB has formatting, table of contents, navigation, metadata, link, or upload validation problems after export.
- EPUB cover not showing
Use this when the cover is missing in a reader, Kindle Previewer, KDP upload, or EPUBCheck-style report. Scan the EPUB to see whether the OPF cover metadata points to the right image or whether the cover needs manual source-tool work.
- Check exported EPUB after Word or DOCX workflow
Use this after a DOCX, Word, Atticus, Vellum, Reedsy, Kindle Create, or InDesign workflow has already exported an EPUB and you need to check why that EPUB may fail KDP, Kindle Previewer, or EPUBCheck.
- EPUBCheck error codes
Use this when EPUBCheck reports RSC, OPF, NCX, or PKG errors and you need to group the code family before editing OPF, nav, NCX, XHTML, resource, anchor, manifest, or ZIP files.
- Invalid, corrupt, or damaged EPUB file
Use this when an EPUB file is called invalid, corrupt, damaged, not a valid EPUB, or unreadable by KDP, Kindle Previewer, EPUBCheck, or a publishing platform.
- Kindle Previewer conversion failed
Use this when Kindle Previewer fails, conversion fails, enhanced typesetting cannot continue, or the preview step reports EPUB validation, TOC, metadata, link, or package problems.
- Apple Books or Google Play rejected EPUB
Use this when Apple Books, Google Play Books, Draft2Digital, or another store rejects an EPUB that may still open locally or pass a looser upload workflow.
- Draft2Digital, Kobo, B&N, or IngramSpark EPUB rejected
Use this when Draft2Digital, Smashwords, Kobo Writing Life, Barnes & Noble Press, or IngramSpark rejects an EPUB and you need to know whether the file has a standard EPUB structure blocker before another upload.
Find the error you see
Broken references and anchors
Start here when EPUBCheck or KDP points to a missing image, stylesheet, chapter file, internal link with a missing anchor, 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 anchors and #id targets before you retry the EPUB.
- Referenced resource could not be found or OPF_010
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 KDP, Kindle Previewer, or EPUBCheck reports RSC_012, broken internal links, missing anchors, or a TOC target that exists as a file but not as an id after #.
- 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, images are mislabeled, 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 and EPUBCheck reports OPF_030 unique-identifier was not found. Match the package unique-identifier to a real dc:identifier before another KDP upload.
- EPUB metadata checker
Use this when you need to check EPUB metadata structure in content.opf, including unique identifiers, language, modified date, manifest links, and package fields that can block validation.
- dcterms:modified missing in EPUB
Use this when EPUBCheck, Kindle Previewer, or a publishing platform points to missing, duplicated, or malformed dcterms:modified metadata in the OPF package file.
- More than one title defined in OPF metadata
Use this when EPUBCheck or a publishing platform says the OPF metadata has more than one title. Check the metadata before changing KDP listing details.
- 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.
- PKG_021 corrupted image file encountered
Use this when EPUBCheck reports PKG_021 or says a corrupted image file was encountered. Locate the packaged image before editing OPF or rebuilding the EPUB.
- PKG_022 wrong file extension for image
Use this when EPUBCheck reports PKG_022 or says an image has the wrong file extension. Compare the packaged image bytes, extension, and OPF manifest media type.
- OPF_003 or RSC_008 item is not declared in the OPF manifest
Use this when a file exists in the EPUB but content.opf does not declare it, nav.xhtml is present but not wired as navigation, or EPUBCheck says a referenced resource is not declared in the OPF manifest.
- 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.
- EPUB cover-image property is missing
Use this when the EPUB cover image exists but the OPF manifest does not mark it with the EPUB 3 cover-image property.
- PKG_007 mimetype file contents invalid or compressed
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_002 OPF file not found in the EPUB
Use this when EPUBCheck reports OPF_002, 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.
- RSC_002 container.xml missing in EPUB
Use this when KDP or EPUBCheck reports RSC_002, META-INF/container.xml is missing, or the container map is not usable. Confirm the real OPF package path before rebuilding the EPUB container map.
- RSC_003 no rootfile tag in container.xml
Use this when EPUBCheck says container.xml has no rootfile tag. Check the EPUB package map before you edit chapters, metadata, or KDP settings.
- OPF_019 spine tag was not found
Use this when EPUBCheck reports OPF_019 or says the OPF spine is missing. Check the package reading order before changing nav.xhtml, toc.ncx, or chapter files.
- PKG_006 EPUB mimetype file missing or not first
Use this when KDP or EPUBCheck reports PKG_006, or when manual zipping or repackaging may have moved or compressed the EPUB mimetype file. Check the root-level ZIP order before rebuilding the archive.
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.
- Have a cover design, crop, white-border, compression, paperback PDF, spine, bleed, barcode, or Canva export problem? Fix that in the cover or design workflow instead.
- Need DRM removal, cover artwork changes, typography, book formatting, or KDP account help? That work happens outside the EPUB structure scan.