VAST-2.0-unknown-attribute
VAST-2.0-unknown-attribute
Element has an attribute not defined in the VAST spec
WarningSchemaIAB VAST 2.0 §2VAST 2.0 and later (all versions)
Short answer
An attribute was found on a VAST element that is not part of the spec for that element. This is usually a typo or a proprietary extension that should be inside an <Extension> block.
Why this matters in production
This rule is a strong risk signal. Tags with this issue often still parse, but they become brittle across SDKs, SSAI resolvers, and CTV environments. Schema violations tend to create parser disagreement. One system may recover while another drops the tag entirely, which is why these bugs often show up as environment-specific fill loss. Affected scope: VAST 2.0 and later (all versions).
How to fix
Remove the unrecognised attribute, or move proprietary data inside an <Extension> block.
Check your VAST tag for
VAST-2.0-unknown-attribute and other issues instantly.Open the VAST tag validator →Other Schema rules
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