# EPUBCheck NCX-001: NCX identifier (…) does not match OPF…

Source: https://epublab.com/epubcheck/ncx-001/ (updated 2026-11-03)

EPUBCheck NCX-001 is an error message: “NCX identifier ("…") does not match OPF identifier ("…").” The NCX's dtb:uid does not match the package's unique identifier.

- Official message (EPUBCheck 5.4.0): NCX identifier ("%1$s") does not match OPF identifier ("%2$s").
- Default severity: Error

## Typical causes

- The book's identifier was changed in the package document but not in the NCX.

## How to fix it

- Copy the value of the dc:identifier named by unique-identifier into the NCX meta name="dtb:uid".

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EPUBLab.