vastlint
VAST-2.0-parse-error

VAST-2.0-parse-error

XML parse error — document may be malformed

ErrorConsistencyIAB VAST 2.0 §2VAST 2.0 and later (all versions)

Short answer

The VAST document is not well-formed XML. This usually means unclosed tags, unescaped </& characters outside CDATA, or invalid encoding. Virtually every player will reject a malformed XML document outright.

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. Consistency rules catch documents that technically contain the right pieces but combine them in ways that produce conflicting signals for downstream systems. Affected scope: VAST 2.0 and later (all versions).

How to fix

Fix the XML syntax error: close all open tags, escape <, >, and & outside CDATA as &lt;, &gt;, &amp;, and confirm the declared encoding matches the file encoding.

Invalid

<VAST version="4.0">
  <Ad id="1">
    <InLine>
      <AdTitle>My Ad & Promo</AdTitle>  <!-- & must be &amp; outside CDATA -->
    </InLine>
  </Ad>
</VAST>

Valid

<VAST version="4.0">
  <Ad id="1">
    <InLine>
      <AdTitle>My Ad &amp; Promo</AdTitle>
    </InLine>
  </Ad>
</VAST>
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Other Consistency rules

VAST-2.0-version-mismatchDeclared version does not match structural signalsVAST-2.0-duplicate-impressionDuplicate <Impression> URL within the same <Ad>