Back to Error DirectoryW3C EPUBCheck Standard
RSC-028Critical Ingestion Error

XML documents must be encoded in UTF-8, but resource was detected.

XML documents must be encoded in UTF-8, but resource was detected.

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Fix all RSC-028 errors in your EPUB automatically

PreFlight checks for RSC-028 issues in memory and provides 1-click remediation during client-side packaging.

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What This Error Means in Plain English

EPUBCheck detected XML documents must be encoded in UTF-8, but resource was detected.. 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 RSC-028: XML documents must be encoded in UTF-8, but resource was detected.

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule RSC-028 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the RSC-028 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.