PKG-007 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 and ZIP container

EPUBCheck PKG-007: wrong mimetype file content

Updated: Nov 4, 2026

EPUBCheck PKG-007 is an error message: “The content of the mimetype file must be the string "application/epub+zip"….” The mimetype file must contain exactly the text application/epub+zip, with nothing before or after it. EPUB 3.3 forbids leading or trailing whitespace and a byte order mark in that file.

The official message

The content of the mimetype file must be the string "application/epub+zip"%1$s

Variants

whitespace: with no whitespace or newline.

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 trailing newline or space added by a text editor.
A different value, such as a typo or another media type.
A byte order mark (BOM) added by an editor that saves UTF-8 with BOM.

How to fix it

Recreate the file without a newline, for example with printf 'application/epub+zip' > mimetype.
Rebuild the archive with mimetype first: Rebuild the archive with the mimetype file first and stored uncompressed, for example from the folder that contains the book: zip -X0 book.epub mimetype and then zip -rX9 book.epub META-INF OEBPS (use your own folder names).
Validate again.

When it's not this

If the file is missing or not first in the archive, that is PKG-006.

Terms used here

What is the EPUB container (OCF)?

Other PKG messages

PKG-006 Mimetype file entry is missing or is not the first file in the archive.
PKG-008 Unable to read file "…".
PKG-005 The mimetype file has an extra field of length …. The use of the extra field feature of the ZIP format is not permitted for the mimetype file.
PKG-009 The file name "…" contains characters that are not allowed in OCF file names: ….
PKG-004 Corrupted EPUB ZIP header.
PKG-010 The file name "…" contains spaces, which may create interoperability issues with older reading systems.

Sources

EPUB 3.3, §4.3.3 OCF ZIP container media type identification · read Nov 4, 2026

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