VASTlint

VAST examples / Document structure

An <Ad> containing both <InLine> and <Wrapper>

VAST 2.01 error1 warningVAST-2.0-ad-has-inline-or-wrapper

The scenario

A header-bidding wrapper vendor was merging responses from two upstream systems into a single ad object during a migration. The intent was a clean fallback, but the build accidentally emitted one <Ad> carrying both branches.

The broken tag

<?xml version="1.0" encoding="UTF-8"?>
<!-- ERROR: VAST-2.0-ad-has-inline-or-wrapper — <Ad> contains BOTH <InLine> and <Wrapper> -->
<VAST version="2.0">
  <Ad id="ad-001">
    <InLine>
      <AdSystem>Test</AdSystem>
      <AdTitle>Test Ad</AdTitle>
      <Impression><![CDATA[https://track.example.com/impression]]></Impression>
      <Creatives>
        <Creative>
          <Linear>
            <Duration>00:00:30</Duration>
            <MediaFiles>
              <MediaFile delivery="progressive" type="video/mp4" width="1920" height="1080">
                <![CDATA[https://cdn.example.com/video.mp4]]>
              </MediaFile>
            </MediaFiles>
          </Linear>
        </Creative>
      </Creatives>
    </InLine>
    <Wrapper>
      <AdSystem>Test Wrapper</AdSystem>
      <Impression><![CDATA[https://track.example.com/wrapper-impression]]></Impression>
      <VASTAdTagURI><![CDATA[https://ad.example.com/vast.xml]]></VASTAdTagURI>
    </Wrapper>
  </Ad>
</VAST>

What the validator reports

Running this tag through vastlint produces the following. The primary failure for this example:

errorVAST-2.0-ad-has-inline-or-wrapperIAB VAST 2.0 §2.2line 4

<Ad> must not contain both <InLine> and <Wrapper>

The same tag also surfaces these secondary findings — real tags rarely fail in isolation:

warningVAST-2.0-linear-tracking-quartilesIAB VAST 4.1 §3.14.2line 11

<Linear> has no standard quartile tracking events (start/firstQuartile/midpoint/thirdQuartile/complete) — ad will serve but measurement system receives no signal

Why it breaks

The <Ad> element contains both an <InLine> and a <Wrapper> child. The spec is explicit that an Ad must contain exactly one of the two — either a self-contained InLine ad or a Wrapper that redirects to another VAST document, never both. The two represent mutually exclusive resolution paths, and a consumer cannot know which one is authoritative.

What it costs

Faced with an ambiguous Ad, players diverge: some take the InLine, some follow the Wrapper, some reject the whole Ad. That nondeterminism produces inconsistent creative delivery and tracking across the audience, corrupts attribution, and makes A/B reads unreliable. Strict consumers drop the Ad entirely, causing no-fill on a portion of traffic.

The fix

Split the two into separate <Ad> elements, or emit only the branch you intend. If you want fallback, use distinct Ads (optionally in a sequence/pod) rather than mixing InLine and Wrapper in one Ad.

<!-- one Ad = exactly one of InLine OR Wrapper -->
<Ad id="primary"><Wrapper>...</Wrapper></Ad>
<Ad id="fallback"><InLine>...</InLine></Ad>

VAST XML fragment only. This excerpt belongs inside a complete VAST document, so standalone validation will fail until it is wrapped in a full <VAST>response.

Check your own version of this tag

Paste the resolved XML to run the same spec check, test a live tag URL, or inspect the wrapper chain hop by hop.

Validate this XML →Test this live URL →Inspect this wrapper chain →

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