VAST error codes / Parsing and schema
VAST error 100: XML parsing error
Short answer: The player could not parse the VAST document as XML.
What it means
The response never got far enough to be treated as VAST. The XML itself is malformed, so the player stops before reading any ad.
Common causes
- Unescaped `&`, `<`, or `>` in a URL that was not wrapped in CDATA
- Broken or unterminated `<![CDATA[ ... ]]>` sections
- Mismatched or unclosed tags, or invalid nesting
- A truncated response, or HTML (an error page) returned instead of XML
How to fix it
Paste the raw response into the validator. A 100 is almost always a structural XML problem the validator points to by line, not a VAST-semantics problem.
VAST error codes are runtime buckets emitted by the player. They tell you where the failure happened, not which line of XML caused it. Paste the raw tag into the validator to map this code onto the exact element and rule.
Related vastlint rules
- VAST-2.0-root-element: Root element must be <VAST>
Related error codes
Debug this tag now
Validate the XML, follow the wrapper chain, or check it in CI before launch:
# CLI: exits non-zero on errors, ideal for pipelines
vastlint check creative.xmlUse the right tool for this failure
If you already have the resolved XML, run a pure spec check. If you only have a live tag URL, test that endpoint first. If the failure happens in the wrapper chain, inspect each hop.