OPF-005 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-005`

Updated: Nov 3, 2026

EPUBCheck OPF-005 is an error message: “Invalid prefix declaration: URI for prefix "…" doesn’t exist.” A prefix in the prefix attribute has no URI after it.

The official message

Invalid prefix declaration: URI for prefix "%1$s" doesn’t exist.

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 mapping cut short, such as "ibooks:" at the end of the attribute.
Hand-edited or tool-generated package documents that write the prefix attribute with the wrong separators.

How to fix it

The prefix attribute on the package element maps short prefixes to vocabulary URIs, as space-separated pairs like prefix="ibooks: http://vocabulary.itunes.apple.com/rdf/ibooks/vocabulary-extensions-1.0/". Add the vocabulary URI after the prefix, or remove the prefix.
Reserved prefixes such as dcterms, rendition and schema need no declaration at all.

Terms used here

Other OPF messages

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 (":").
OPF-004d Invalid prefix declaration: prefix "…" must be separated by its URI with a space.
OPF-004e Invalid prefix declaration: found illegal whitespace between prefix and URI.

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