EPUBCheck reference
EPUBCheck Error Codes
Use the code to find the right topic, but use the complete message, file path, line, and column to decide what actually needs repair.
Some codes identify broad parser or schema categories. Two reports with the same code can require different fixes.
Repair notes from real reports
- HTM-004: Irregular DOCTYPE
The document declaration does not match the content rules EPUBCheck is applying. EPUB 2 and EPUB 3 use different syntax expectations.
- OPF-054: Invalid date value
A package metadata date is not in an accepted W3C/ISO-style format.
- RSC-005: Error while parsing file
A resource could not be parsed or failed its schema. The remaining message identifies the invalid structure.
After every fix
Validate the complete EPUB again. A passing EPUBCheck result confirms specification-level validity, but it does not guarantee acceptance by Amazon KDP or another retailer.