VAST macros / Ad and pod
[TRANSACTIONID] VAST macro
Short answer: A unique identifier for this ad request transaction. Introduced in VAST 4.1.
What it means
Resolves to a per-request identifier that ties the bid, the ad response, and the resulting tracking events together across systems.
Example value
After the player substitutes the macro, [TRANSACTIONID] becomes something like:
txn-9f8e7d6c5b4aWhere it is valid
Impression, tracking, and click URLs.
Macros are case-sensitive and substituted only inside URL fields. A macro written in the wrong case, or placed where it has no defined value, is sent to the server as literal text instead of a value.
Using it in a tag
<Impression><![CDATA[https://t.example.com/i?val=[TRANSACTIONID]&cb=[CACHEBUSTING]]]></Impression>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.
Related vastlint rules
- VAST-2.0-macro-unknown: URL contains a [MACRO] that is not a recognised IAB VAST macro
- VAST-2.0-macro-lowercase: Recognised macro is not uppercase — players match macro names case-sensitively
Related macros
- [ADSERVINGID]: The unique ad-serving identifier shared across the supply chain.
- [UNIVERSALADID]: The creative's UniversalAdId (registry and value).
Validate your macros
vastlint flags unknown, mis-cased, deprecated, out-of-context, and unencoded macros in any tracking, click, error, impression, or media URL:
# CLI: exits non-zero on errors, ideal for pipelines
vastlint check creative.xmlUse the right tool for this failure
If you already have the resolved XML, run a pure spec check. If you only have a live tag URL, test that endpoint first. If the failure happens in the wrapper chain, inspect each hop.