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EPUBCheck · Package and ZIP container

PKG-024

Updated:

EPUBCheck PKG-024 is a usage message: “Uncommon EPUB file extension.” The file does not end in .epub, so some reading apps and stores may not recognise it.

The official message

Uncommon EPUB file extension.

EPUBCheck's suggestion: For maximum compatibility, use ".epub".

Default severity
Usage. Informative only and hidden by default: it appears when EPUBCheck runs with -u (--usage). It does not make the EPUB invalid.
EPUBCheck version
5.4.0

Typical causes

  • A file saved with another extension, or a double extension added by a download or email client.

How to fix it

  • Rename the file to end in .epub. Nothing inside the EPUB needs to change.

Terms used here

Other PKG messages

  • PKG-025 Publication resource must not be located in the META-INF directory
  • PKG-022 Wrong file extension for image. The image is a "…" file but has the file extension "…".
  • PKG-026 Obfuscated resource must be a Font Core Media Type (was declared as "…" in "…").
  • PKG-021 Corrupted image file encountered.
  • PKG-027 Could not extract EPUB ZIP content, probably due to file names not encoded in UTF-8.
  • PKG-017 Uncommon EPUB file extension.

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

FAQ

What does EPUBCheck PKG-024 mean?

EPUBCheck PKG-024 is a usage message: “Uncommon EPUB file extension.” The file does not end in .epub, so some reading apps and stores may not recognise it.

Is PKG-024 an error?

PKG-024 is reported as usage by default. Informative only and hidden by default: it appears when EPUBCheck runs with -u (--usage). It does not make the EPUB invalid.