Match the report title.
Look for "EPUB validation scan" or the closest title above. Keep the original EPUBCheck, KDP, or Kindle Previewer wording if it differs.
EPUB error guide
Free EPUB validator and checker
Use this as a free EPUB checker when you need to know whether a reflowable EPUB has package, metadata, navigation, link, anchor, or ZIP errors before another publishing upload.
You see
A validator, KDP, or Previewer error.
Upload the exported reflowable EPUB when you need the internal path, issue family, and repair decision.
You get
A scan report, not a score.
The report shows affected OPF, nav, XHTML, image, manifest, container, or ZIP paths and whether a checked repair is possible.
Do not upload
Source, design, or policy problems.
Use another workflow for DOCX/PDF conversion, cover design, fixed-layout books, DRM, KDP listing issues, or platform approval questions.
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
- EPUB validation scan
- KDP upload blocker check
- EPUBCheck structural errors
- Package, metadata, navigation, link, or ZIP issue
Use this guide when
Your message matches "EPUB validation scan" 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 EPUB checker report should show.
A useful report should connect the validator message to the internal EPUB part that needs attention.
Package file
OEBPS/content.opf, OEBPS/nav.xhtml, toc.ncx, chapter XHTML, CSS, image, or META-INF/container.xml.
Issue family
Missing resource, broken anchor, OPF metadata, manifest, navigation, or ZIP packaging.
Original message
The KDP, Kindle Previewer, or EPUBCheck wording that blocked the upload.
Decision
Repairable, needs manual review, or unsupported by this scanner.
Recheck
A repaired EPUB is offered only when the fixed file passes EPUBCheck again.
The goal is not a generic score. The useful output is whether this EPUB has a concrete blocker and what you can do next.
2. Next step
Use the scan to choose validation, repair, or manual review.
Broad EPUB checker searches can mean different jobs. Keep the next step tied to the actual file result.
Upload scan
Use this when you have a finished .epub file.
Upload the file you plan to send to KDP, Kindle Previewer, EPUBCheck, or another publishing workflow.
Checked repair
Use this when the report finds one clear structural fix.
The repair can happen only when the correct package, metadata, manifest, navigation, path, or ZIP change is unambiguous.
Manual review
Use this when the issue depends on author intent.
Return to the source tool or EPUB editor when the fix would choose chapter order, TOC titles, missing assets, visible layout, or book content.
3. Concrete path example
A validator-style report should point to a real EPUB path.
The path is what turns a broad validation failure into something you can inspect.
Validator result: EPUBCheck reports OPF_030 and RSC_007 messages. Report: Primary blocker: OPF unique-identifier points to a missing dc:identifier id Affected path: OEBPS/content.opf Related issue: OEBPS/nav.xhtml points to one missing image path Decision: repair OPF identifier only if one metadata id is clear; review missing image manually
Do not treat every validation error as auto-fixable. Some errors are only safe to locate and explain.
Quick decision
Decide whether this is an EPUB structure problem.
A broad EPUB checker page should filter users without hiding the current tool boundary.
Good fit
You already have a reflowable .epub file.
The scanner can inspect EPUB 2/3 package structure, metadata, navigation, links, anchors, manifest entries, and ZIP packaging.
Not this tool
You need conversion or book formatting.
DOCX to EPUB, PDF to EPUB, cover design, typography, fixed-layout books, comics, and KDP account issues belong in the source or publishing workflow.
Useful anyway
You are not sure what failed.
If the file is a normal EPUB, the report can still tell you whether the problem is repairable here, needs manual review, or is outside scope.
Start here
Check the exported EPUB, not the source manuscript.
An EPUB validator can tell you whether the packaged book is structurally valid. Upload the .epub you plan to retry so the report can inspect the package paths, OPF metadata, manifest, spine, navigation, links, anchors, and ZIP wrapper.
What it means
An EPUB is a ZIP package with metadata, a file list, reading order, navigation files, chapter XHTML, CSS, images, anchors, and a container map. Validation checks whether those parts agree with each other.
Can it be fixed automatically?
EPUB Fixer can help when the EPUB contains one clear structural correction, such as an OPF identifier link, manifest entry, media type, navigation declaration, path mismatch, or ZIP packaging rule that can be changed and checked again.
What to check next
Confirm the file is a real .epub, not a DOCX, PDF, KPF, KCB, or renamed ZIP file.
What not to assume
It does not convert source files, design a book, rewrite content, pick chapter order, create missing assets, guarantee platform approval, or repair fixed-layout, DRM, comic, image-first, KPF, KCB, DOCX, or PDF inputs.
Common situations
Common reasons people look for an EPUB validator.
Start from the file state you have now, then choose whether to upload or use a narrower guide.
KDP rejected the EPUB but the book opens locally.
Reader apps can tolerate broken references that KDP, Kindle Previewer, or EPUBCheck rejects.
Scan the exported EPUB and start with the affected path in the report.
You want to check the EPUB before another publishing upload.
The scan can catch package, metadata, navigation, link, anchor, manifest, and ZIP problems before another retry.
Use the report as a preflight, then retry only after the blocking issue is understood.
You converted or exported an EPUB from another tool.
Export tools can produce files that open locally but still have strict validation problems.
Upload the EPUB output, not the DOCX, PDF, or source project.
Validator phrases this page can help with
EPUB validator / EPUB checker: scan a reflowable EPUB 2/3 package for KDP, Kindle Previewer, and EPUBCheck structural blockers.
Where EPUB validation problems usually appear
Authors, formatters, and small publishers search for an EPUB validator when an upload fails, Kindle Previewer reports validation problems, EPUBCheck returns RSC / OPF / PKG errors, or an exported EPUB needs a publishing-readiness check.
What it means
The EPUB can open in a reader while still failing strict validation.
An EPUB is a ZIP package with metadata, a file list, reading order, navigation files, chapter XHTML, CSS, images, anchors, and a container map. Validation checks whether those parts agree with each other.
Common failures include missing referenced resources, broken anchors, disconnected navigation, wrong OPF identifiers, missing manifest items, media-type mismatches, incorrect container.xml paths, and ZIP wrapper mistakes.
Before you edit
Check the package paths before changing the book.
Use the scan report to find the file, field, or package rule behind the validator message. Do not edit the manuscript, rebuild the TOC, or rename assets until the affected EPUB path is clear.
- 1Confirm the file is a real .epub, not a DOCX, PDF, KPF, KCB, or renamed ZIP file.
- 2Save the KDP, Kindle Previewer, or EPUBCheck message if you already have one.
- 3Scan the exported EPUB and look for the affected path, issue family, and repair decision.
- 4Check whether the problem is package wiring, a missing target file, a missing anchor, OPF metadata, navigation, manifest, media type, container.xml, or ZIP packaging.
- 5Use automatic repair only when the report shows one clear structural change and the repaired file passes EPUBCheck again.
- 6Return to the source tool or EPUB editor when the report says manual review or unsupported.
Why KDP checks it
Why EPUB validators and publishing platforms check these files.
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 a validator issue can be repaired safely.
When automatic repair is safe
EPUB Fixer can help when the EPUB contains one clear structural correction, such as an OPF identifier link, manifest entry, media type, navigation declaration, path mismatch, or ZIP packaging rule that can be changed and checked again.
When you need manual review
It does not convert source files, design a book, rewrite content, pick chapter order, create missing assets, guarantee platform approval, or repair fixed-layout, DRM, comic, image-first, KPF, KCB, DOCX, or PDF inputs.
Before / after example
Before: content.opf points to an identifier id that does not exist. After: the unique-identifier can be aligned when one real dc:identifier is clear and EPUBCheck passes again. Before: a chapter points to a missing image that is not packaged anywhere; restore the source asset instead.
Ready to retry?
Upload the EPUB for a validator-style scan.
The scan runs against the EPUB package and keeps the result practical: affected path, issue family, repair decision, and whether a checked repair can be downloaded after another EPUBCheck pass.
Upload EPUB to scanFAQ
Questions authors ask about free EPUB validators.
Is EPUB Fixer a free EPUB validator?
It works as a free EPUB structure checker for reflowable EPUB files. It focuses on KDP, Kindle Previewer, and EPUBCheck blockers rather than giving a broad quality score.
Can I upload a DOCX or PDF to validate it?
No. Export or convert the source into a real .epub first, then upload the EPUB output if KDP, Kindle Previewer, or EPUBCheck rejects it.
Does the scan guarantee KDP approval?
No. It can locate and sometimes repair EPUB structure blockers, then check the repaired EPUB with EPUBCheck again. KDP account, content, listing, review, and policy decisions are outside this scanner.
How is this different from raw EPUBCheck output?
EPUBCheck reports rule errors. EPUB Fixer adds the affected path, issue family, repairability decision, and next step so you know whether to repair, review manually, or stop.