vastlint
VAST-2.0-creative-unknown-child

Creative can only contain valid VAST child elements

<Creative> contains an unrecognised child element

ErrorSchemaIAB VAST 2.0 §2.3VAST 2.0 and later (all versions)

Short answer

If <Creative> contains an unsupported child element, the entire creative block becomes invalid. Keep only valid children such as Linear, NonLinearAds, CompanionAds, UniversalAdId, or CreativeExtensions.

`<Creative>` may only contain `<Linear>`, `<NonLinearAds>`, `<CompanionAds>`, `<UniversalAdId>`, and `<CreativeExtensions>`. Any other child is a schema error.

Why this matters in production

This rule is usually a delivery blocker. Many players, SDKs, and ad servers will discard the response or skip the affected creative once this condition is hit. 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 child from <Creative>, or move proprietary data into a <CreativeExtensions> block.

Invalid

<Creative>
  <FooBar />
</Creative>

Valid

<Creative>
  <CreativeExtensions>
    <CreativeExtension><![CDATA[custom creative metadata]]></CreativeExtension>
  </CreativeExtensions>
</Creative>
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Other Schema rules

VAST-2.0-text-only-elementText-only element contains a child elementVAST-2.0-unknown-attributeElement has an attribute not defined in the VAST specVAST-2.0-inline-unknown-child<InLine> contains an unrecognised child elementVAST-2.0-wrapper-unknown-child<Wrapper> contains an unrecognised child elementVAST-2.0-creatives-unknown-child<Creatives> may only contain <Creative> elementsVAST-2.0-linear-unknown-child<Linear> contains an unrecognised child elementVAST-2.0-trackingevents-unknown-child<TrackingEvents> may only contain <Tracking> elementsVAST-2.0-mediafiles-unknown-child<MediaFiles> contains an unrecognised child element