VAST error codes / Parsing and schema
VAST error 101: VAST schema validation error
Short answer: The document is valid XML but does not match the VAST schema.
Debug this tag now
If you only have a live URL, test it first. If the failure is in the wrapper chain, inspect each hop. Validate resolved XML when you already have the response.
What your player reported
101· VAST schema validation error.
Wording from the IAB VAST 4.3 specification error table. Players may shorten or reformat it, but the code is the same.
What it means
The XML parses, but the structure is not legal VAST: a required element is missing, or elements are in the wrong place for the declared version.
Common causes
- Missing required elements such as `<AdSystem>`, `<Impression>`, or `<Creatives>`
- Elements nested under the wrong parent
- Attributes or children that do not exist in the declared VAST version
How to fix it
Validate against the declared version. vastlint reports the exact missing or misplaced element and the spec reference it comes from.
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-inline-adsystem: <InLine> must contain <AdSystem>
- VAST-2.0-inline-impression: <InLine> must contain at least one <Impression>
- VAST-2.0-inline-creatives: <InLine> must contain <Creatives> with at least one <Creative>
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.xml