Back to Error DirectoryW3C EPUBCheck & Amazon KDP
HTM-004Critical Ingestion Error

Unclosed XML Tag / Malformed XHTML Document

An XHTML chapter contains an unclosed tag or malformed XML syntax.

Automated 1-Click Fix Ready

Fix all HTM-004 errors in your EPUB automatically

PreFlight uses the browser's native DOMParser to detect XML syntax anomalies, sanitizes malformed tag nesting, and outputs valid, well-formed XHTML.

Scan & Fix Now

What This Error Means in Plain English

Unlike regular web pages that can forgive missing closing tags, EPUB chapters are strict XML. A single missing </p>, </div>, or unclosed <br> causes the entire chapter to fail parsing and crash reading systems.

Why Retailers & EAA Regulations Block This File

XML parser errors immediately abort automated book ingest pipelines across all digital distributors.

Technical Specification: The XML parser throws a fatal 'parsererror' exception when encountering mismatched opening/closing elements or unquoted attribute values.

Manual Fix Instructions (for Sigil / Calibre)

  1. Open the flagged file in a code editor with XML validation.
  2. Locate the line reported in the error message.
  3. Ensure all void elements are self-closed (<br />, <hr />, <img />) and every open tag has an exact closing counterpart.