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Glossary

What is the NCX table of contents?

Updated:

The NCX (Navigation Control file for XML) is the table of contents format of EPUB 2, an XML file with the media type application/x-dtbncx+xml. EPUB 3 replaced it with the HTML navigation document but still allows an NCX for older readers.

Why it matters when you convert a PDF to EPUB

An EPUB 3 made from a PDF needs a navigation document; adding an NCX as well only helps very old reading systems. If an NCX is present, its identifier must match the package's unique identifier, which is a frequent EPUBCheck error after editing metadata by hand.

How EpubCC handles it: it does not write an NCX. Its EPUB 3 output carries only the HTML navigation document, which is what current reading apps read; a very old device that only understands EPUB 2 may show no table of contents. Leaving the NCX out also avoids the identifier mismatches that EPUBCheck reports when the NCX and the package disagree.

Related terms

EPUBCheck messages about this

  • NCX-001 NCX identifier ("…") does not match OPF identifier ("…").
  • NCX-006 Empty "text" label in the NCX document
  • OPF-050 TOC attribute references resource with non-NCX mime type; "application/x-dtbncx+xml" is expected.
  • NAV-001 The nav file is not supported for EPUB v2.
  • NCX-004 NCX identifier ("dtb:uid" metadata) should not contain leading or trailing whitespace.
  • OBS-001 Usage of … is outdated.

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FAQ

What is the NCX table of contents?

The NCX (Navigation Control file for XML) is the table of contents format of EPUB 2, an XML file with the media type application/x-dtbncx+xml. EPUB 3 replaced it with the HTML navigation document but still allows an NCX for older readers.