VAST macros / Cachebusting and error
[CACHEBUSTING] VAST macro
Short answer: A random value that prevents caching of a tracking request. Introduced in VAST 3.0.
What it means
Resolves to a random 8-digit number generated fresh for each request, so caches and proxies do not collapse repeated tracking calls into one.
Example value
After the player substitutes the macro, [CACHEBUSTING] becomes something like:
48261537Where it is valid
Any impression, tracking, or click URL.
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=[CACHEBUSTING]&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
- [TIMESTAMP]: The ISO 8601 timestamp when the macro is replaced.
- [TRANSACTIONID]: A unique identifier for this ad request transaction.
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.