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Answer

How do I fix EPUBCheck errors?

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Run EPUBCheck, then fix the messages in order: each one gives a code such as RSC-005, the file, the line and column, and fixing the first errors often clears several later ones. Look up the code in our [EPUBCheck reference](/epubcheck/) for its usual causes and fix, edit the EPUB's files, rebuild the archive and validate again until no errors remain.

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Step by step

  • Run java -jar epubcheck.jar book.epub (EPUBCheck is free, from the W3C). Add --locale en if you want the messages in English whatever your system language.
  • Start with fatal errors and errors; warnings do not make the EPUB invalid.
  • For each message, open the file it names at the line and column it gives. Look up the code to know what it means.
  • Unzip the EPUB, or open it in an EPUB editor, and correct the file.
  • Rebuild the archive with the mimetype file first and uncompressed, then validate again.

The most common codes

  • RSC-005: a file breaks the schema, for example an attribute not allowed where it is or a missing dcterms:modified date.
  • RSC-007 and RSC-008: a referenced file is missing, or present but not in the manifest.
  • RSC-012: a link points to an #id that does not exist, often after footnotes were moved.
  • OPF-014 and PKG-006: a missing manifest property, or a mimetype file that is not first in the ZIP.

When the EPUB came from a converter

If a converter produced hundreds of errors, fixing them by hand is rarely worth it: convert again with a tool that writes valid EPUB 3. EpubCC writes EPUB 3, and every EPUB in our public benchmark was validated with EPUBCheck.

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FAQ

How do I fix EPUBCheck errors?

Run EPUBCheck, then fix the messages in order: each one gives a code such as RSC-005, the file, the line and column, and fixing the first errors often clears several later ones. Look up the code in our [EPUBCheck reference](/epubcheck/) for its usual causes and fix, edit the EPUB's files, rebuild the archive and validate again until no errors remain.

Do warnings need fixing?

Warnings do not make an EPUB invalid and EPUBCheck exits with status 0, unless you run it with --failonwarnings. They point to things that may cause trouble in some reading apps.

Why does EPUBCheck show messages I don't see in my editor?

Usage messages are hidden by default and only appear with -u (--usage). They are informative and do not make the file invalid.

Does a valid EPUB guarantee it looks good?

No. EPUBCheck checks the rules of the format, not whether paragraphs, headers or notes were recovered well from the PDF.