vastlint
VAST-4.3-js-resource-browser-optional

VAST-4.3-js-resource-browser-optional

<JavaScriptResource> should have a browserOptional attribute

WarningRequired fieldsIAB VAST 4.3 §2.3VAST 4.3 only

Short answer

In VAST 4.3, <JavaScriptResource> elements should indicate whether they are browser-optional via the browserOptional attribute. This matters for CTV/audio environments that lack a browser JS runtime.

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. Required-field failures usually stop validation early because the platform cannot determine the basic shape of the ad, the creative metadata, or the mandatory tracking payload. Affected scope: VAST 4.3 only.

How to fix

Add browserOptional="true" if the script can be skipped in non-browser environments (CTV, audio), or browserOptional="false" if it is required.

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Other Required fields rules

VAST-2.0-root-elementRoot element must be <VAST>VAST-2.0-root-version<VAST> must have a version attributeVAST-2.0-root-version-valueVAST version attribute must be a recognised version stringVAST-2.0-root-has-ad-or-error<VAST> must contain at least one <Ad> or <Error>VAST-4.0-wrapper-root-error<VAST> root contains both <Ad> and <Error> elements (invalid per VAST 4.0)VAST-2.0-ad-has-inline-or-wrapperEach <Ad> must contain exactly one <InLine> or <Wrapper>VAST-2.0-inline-adsystem<InLine> must contain <AdSystem>VAST-2.0-inline-adtitle<InLine> must contain <AdTitle>