# What is the NCX table of contents?

Source: https://epublab.com/glossary/ncx/ (updated 2026-11-03)

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.