EPUB FixerKDP upload error scanner

EPUB error guide

EPUBCheck online free for KDP preflight

Upload one reflowable EPUB for a free browser-based EPUBCheck-style scan before KDP, Kindle Previewer, or another publishing upload.

Best fit

You want an online EPUBCheck-style preflight.

Upload a reflowable .epub to check common validation blockers without installing the command-line tool.

Report shows

EPUBCheck plus practical routing.

The report keeps validator wording, names affected paths, and separates checked repair from manual review or unsupported cases.

Know the limit

Independent tool, not W3C or KDP.

Use official EPUBCheck, Kindle Previewer, and KDP upload as the final authority for their own workflows.

Scan EPUB structureSee an example report

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 online free
  • Online EPUBCheck for EPUB files
  • Free EPUBCheck validator before KDP upload
  • EPUBCheck online scanner
  • EPUBCheck RSC OPF NCX PKG report
  • Browser-based EPUB structure check

Use this guide when

Your message matches "EPUBCheck online free" 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 online free" 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 online EPUBCheck report should add.

Raw validator output becomes more useful when it is tied to the internal EPUB file and a next action.

Validator code

RSC_007, RSC_012, OPF_030, OPF_003, NCX_001, PKG_006, or another EPUBCheck family.

Affected path

content.opf, nav.xhtml, toc.ncx, chapter XHTML, CSS, image, container.xml, or ZIP entry.

Grouped cause

Missing resource, broken anchor, OPF metadata, manifest, navigation, media-type, container, or ZIP wrapper.

Repair decision

Checked repair only when one structural change is clear and can be validated again.

Final check

Use official EPUBCheck, Kindle Previewer, and KDP upload for final confirmation.

The value is not the word online. The value is seeing what file caused the validation issue and what you should do next.

2. Next step

Choose the next step from the EPUBCheck family.

The code family usually points to the EPUB layer that failed.

RSC

Check links, anchors, and referenced resources.

Start with the source file and target path. Missing files and missing fragments need different fixes.

OPF / NCX

Check package metadata and navigation wiring.

Open content.opf, nav.xhtml, or toc.ncx before editing chapter text.

PKG

Check ZIP wrapper and container files.

Repair mimetype, compression, container.xml, or rootfile issues before deeper validation lines.

3. Concrete path example

Online EPUBCheck output should be grouped before repair.

Several validator lines can come from one package mistake.

EPUBCheck output:
ERROR(OPF-030): unique-identifier target was not found
ERROR(RSC-007): referenced resource could not be found

Report:
Primary group: OPF metadata
Affected path: OEBPS/content.opf
Secondary group: missing resource from OEBPS/nav.xhtml
Decision: repair OPF only if one dc:identifier is clear; review the missing resource separately

A clean-looking online report is not enough if the fix requires choosing missing content or author intent.

Quick decision

Decide whether you need validation output or a repair decision.

Choose the online scan for one file; use the official EPUBCheck CLI or library for repeatable local or batch validation.

Good fit

You need a free online scan of one reflowable EPUB.

The scanner can check common EPUBCheck blockers and return affected paths without a local command-line setup.

Better with CLI

You need official batch validation or build automation.

Use the official EPUBCheck command-line tool or Java library for local, repeatable, or large-scale workflows.

Not this tool

You need platform review or editing work.

KDP review, content review, book formatting, conversion, and visual design are not EPUBCheck repair decisions.

Start here

Use an online scan when installing EPUBCheck is too much for one file.

EPUBCheck is a W3C conformance checker distributed as a command-line tool or Java library. For one EPUB file, this browser scan turns validation output into affected paths and next steps.

Matched

What it means

EPUBCheck checks whether an EPUB follows the EPUB specifications. EPUB Fixer adds a user-facing report that names paths, groups issues, and decides whether a checked repair is possible.

Matched

Can it be fixed automatically?

A checked repair is possible when an EPUBCheck issue maps to one clear package, OPF, manifest, media-type, navigation, reference, anchor, container, or ZIP change that can be validated again.

Matched

What to check next

Upload a real reflowable .epub file, not a source file or renamed archive.

Matched

What not to assume

It cannot replace official EPUBCheck for every workflow, run batch automation, judge book quality, decide KDP review outcomes, convert source files, restore missing content, or decide ambiguous editorial structure.

Common situations

Common EPUBCheck online use cases.

Use the online scan only when it helps you make the next file decision.

Matched

You have one EPUB and do not want to install a CLI.

A browser scan can be enough to see whether the file has common package-level blockers.

Upload the EPUB and keep the report paths for your retry notes.

Matched

You want to check before KDP upload.

KDP recommends validating EPUB files with Kindle Previewer before upload, and EPUBCheck helps catch standard EPUB issues.

Use this scan as a preflight, then still run Previewer or KDP's upload checks.

Matched

You already have raw EPUBCheck output.

Raw output can be long and repetitive when several messages share one root cause.

Scan the EPUB to group messages by affected path and repair boundary.

Matched

You want to know if a validation error can be repaired.

Some errors are safe package wiring fixes; others need missing assets, source export changes, or author judgment.

Follow the report decision instead of assuming every EPUBCheck line is auto-fixable.

EPUBCheck online phrases to check

EPUBCheck online free: scan a reflowable EPUB for RSC, OPF, NCX, PKG, package, metadata, navigation, link, anchor, manifest, media-type, container, and ZIP validation blockers.

Where EPUBCheck online searches usually start

An author, formatter, or publisher searches for EPUBCheck online, free EPUBCheck validator, online EPUB checker, or EPUB validation before KDP upload.

What it means

EPUBCheck output is useful, but authors still need a path-level next step.

EPUBCheck checks whether an EPUB follows the EPUB specifications. EPUB Fixer adds a user-facing report that names paths, groups issues, and decides whether a checked repair is possible.

Common EPUBCheck failures include missing resources, broken anchors, OPF metadata problems, undeclared manifest items, wrong media types, disconnected navigation, NCX mismatches, container.xml errors, and ZIP package mistakes.

Before you edit

Use the scan report to group validation messages.

Do not treat each EPUBCheck line as a separate repair. First group the output by package, OPF, navigation, resource, anchor, media type, container, or ZIP problem.

  1. 1Upload a real reflowable .epub file, not a source file or renamed archive.
  2. 2Read the validator code family first: RSC, OPF, NCX, or PKG.
  3. 3Group repeated messages by affected path before editing.
  4. 4Check whether the report decision is checked repair, manual review, or unsupported.
  5. 5Use checked repair only when a second EPUBCheck pass succeeds.
  6. 6Use official EPUBCheck or Kindle Previewer when you need final tool-specific confirmation.

Why EPUBCheck matters

Why EPUBCheck is the right validation baseline.

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 issue can be repaired here.

When automatic repair is safe

A checked repair is possible when an EPUBCheck issue maps to one clear package, OPF, manifest, media-type, navigation, reference, anchor, container, or ZIP change that can be validated again.

When you need manual review

It cannot replace official EPUBCheck for every workflow, run batch automation, judge book quality, decide KDP review outcomes, convert source files, restore missing content, or decide ambiguous editorial structure.

Before / after example

Before: EPUBCheck reports OPF_030 because the package unique-identifier points to a missing metadata id. After: the id can be aligned when one real dc:identifier is clear and EPUBCheck passes again. Before: RSC_007 points to a missing image that is not packaged; restore the source image.

Ready to retry?

Upload the EPUB for an online EPUBCheck-style scan.

Upload a reflowable .epub. The report shows validator messages, affected EPUB paths, the repair decision, and whether a repaired EPUB passed EPUBCheck again before download.

Upload EPUB to scan

FAQ

Questions authors ask about EPUBCheck online.

Is EPUB Fixer the official EPUBCheck online app?

No. EPUBCheck is a W3C project distributed as a command-line tool or Java library. EPUB Fixer is an independent web tool that uses validation results to show affected paths and repair decisions.

Can I use this instead of installing EPUBCheck?

For a quick scan of one supported EPUB, yes. For batch jobs, CI, local-only workflows, or official repeatable validation, use the EPUBCheck command-line tool.

Does a clean online scan mean KDP will approve my book?

No. It only addresses EPUB structure validation. KDP upload, review, listing, content, account, and policy checks are separate.

Can online EPUBCheck repair errors automatically?

Only when the report finds one safe structural fix and the repaired EPUB passes EPUBCheck again. Missing files, ambiguous anchors, layout, conversion, and source-content issues need manual work.

Related EPUB error guides