OPF-013 is reported as warning by default. The EPUB is still valid, but something is likely to cause problems in some reading apps. EPUBCheck exits with 0 unless you pass --failonwarnings.

EPUBCheck · Package document (OPF)

`OPF-013`

Updated: Nov 3, 2026

EPUBCheck OPF-013 is a warning message: “Resource "…" is declared with MIME type "…" in content, but has MIME type "…" in the package document.” A content document declares one media type for a resource (in a type attribute) and the manifest declares another.

The official message

Resource "%1$s" is declared with MIME type "%2$s" in content, but has MIME type "%3$s" in the package document.

Default severity: Warning. The EPUB is still valid, but something is likely to cause problems in some reading apps. EPUBCheck exits with 0 unless you pass --failonwarnings.
EPUBCheck version: 5.4.0

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

Typical causes

An object, embed, link or source element whose type attribute disagrees with the manifest item.

How to fix it

Make the type attribute and the manifest media-type the same, using the file's real format.

Terms used here

Other OPF messages

OPF-012 Item property "…" is not defined for media type "…".
OPF-014 The property "…" should be declared in the OPF file.
OPF-011 itemref can’t have both page-spread-right and page-spread-left properties.
OPF-015 The property "…" should not be declared in the OPF file.
OPF-016 The element "rootfile" is missing its required attribute "full-path".
OPF-017 The attribute "full-path" on element "rootfile" must not be empty.

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