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EPUBCheck · NCX (EPUB 2 table of contents)

EPUBCheck NCX-006: empty label in the NCX

Updated:

EPUBCheck NCX-006 is a usage message: “Empty "text" label in the NCX document.” An NCX navigation entry has an empty text label, so the table of contents shows a blank line. The NCX is the EPUB 2 table of contents that older reading systems use.

The official message

Empty "text" label in the NCX document

Default severity
Usage. Informative only and hidden by default: it appears when EPUBCheck runs with -u (--usage). It does not make the EPUB invalid.
EPUBCheck version
5.4.0

Typical causes

  • Entries generated from headings that had no text, such as image-only headings.
  • A label removed by hand while the entry was kept.

How to fix it

  1. Open the NCX and find the navPoint whose navLabel text is empty.
  2. Give every navLabel a text, for example <navLabel><text>Chapter 3</text></navLabel>, matching the label in the EPUB 3 navigation document if there is one.
  3. Or remove the entry if it does not lead anywhere useful.
  4. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

When it's not this

An empty label in the EPUB 3 nav document is a schema error reported as RSC-005, not NCX-006.

Terms used here

Other NCX messages

  • NCX-004 NCX identifier ("dtb:uid" metadata) should not contain leading or trailing whitespace.
  • NCX-001 NCX identifier ("…") does not match OPF identifier ("…").

Sources

Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EpubCC.

FAQ

What does EPUBCheck NCX-006 mean?

EPUBCheck NCX-006 is a usage message: “Empty "text" label in the NCX document.” An NCX navigation entry has an empty text label, so the table of contents shows a blank line. The NCX is the EPUB 2 table of contents that older reading systems use.

Is NCX-006 an error?

NCX-006 is reported as usage by default. Informative only and hidden by default: it appears when EPUBCheck runs with -u (--usage). It does not make the EPUB invalid.