OPF-001 is reported as error by default. The EPUB breaks a rule of the specification and is invalid. Stores and Send to Kindle may reject it, and EPUBCheck exits with status 1.

EPUBCheck · Package document (OPF)

`OPF-001`

Updated: Nov 3, 2026

EPUBCheck OPF-001 is an error message: “There was an error when parsing the EPUB version: ….” EPUBCheck could not read the EPUB version from the package document.

The official message

There was an error when parsing the EPUB version: %1$s.

Default severity: Error. The EPUB breaks a rule of the specification and is invalid. Stores and Send to Kindle may reject it, and EPUBCheck exits with status 1.
EPUBCheck version: 5.4.0

%1$s, %2$s… are filled in with the file, value or element EPUBCheck found.

Typical causes

A missing, empty or malformed version attribute on the package element.

How to fix it

Set the version attribute on the package element: version="3.0" for EPUB 3 (EPUB 3.3 still uses 3.0) or version="2.0" for EPUB 2.

Terms used here

Other OPF messages

OPF-002 The OPF file "…" was not found in the EPUB.
OPF-003 Item "…" exists in the EPUB, but is not declared in the OPF manifest.
OPF-004 Invalid prefix declaration: leading or trailing whitespace is not allowed.
OPF-004a Invalid prefix declaration: found empty prefix.
OPF-004b Invalid prefix "…": must be a valid non-colonized name (aka "NCName").
OPF-004c Invalid prefix declaration: prefix "…" must be immediately followed by a colon character (":").

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