Back to Error DirectoryW3C EPUBCheck Standard
OPF-013Critical Ingestion Error

Resource "resource" is declared with MIME type "resource" in conten...

Resource "resource" is declared with MIME type "resource" in content, but has MIME type "resource" in the package document.

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What This Error Means in Plain English

EPUBCheck detected Resource "resource" is declared with MIME type "resource" in content, but has MIME type "resource" in the package document.. Digital reading systems and bookstores require standard conformance to ensure compatibility across all reading apps.

Why Retailers & EAA Regulations Block This File

Automated book distributors (Apple Books, Amazon KDP, Kobo, and IngramSpark) run strict EPUBCheck validation on ingest and reject non-compliant files.

Technical Specification: W3C EPUBCheck rule OPF-013: Resource "resource" is declared with MIME type "resource" in content, but has MIME type "resource" in the package document.

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule OPF-013 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the OPF-013 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.