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Guidance for Uniquely Identifying Creative Asset IDs in VAST (Deprecated)

This guidance is outdated as of June 11, 2024 with the release of the Ad Creative ID Framework which you can review here:


With the release of VAST 4.x, the latest versions of the digital video ad serving template, the Universal Ad-ID feature was introduced to address inconsistencies in how creative identifiers were assigned across various systems. This feature provides a means for an authoritative program such as Ad-ID or any company’s creative ID registration system to act as a registry in assigning a globally unique identifier that can be maintained and tracked across systems. This feature still allows for a creative ID to be included in the adId attribute used in the <Creative> element, with the difference being that the creative ID would be used to specify an ad server’s unique identifier.


While the <UniversalAdID> element is required for VAST 4.x, the spec states that the attribute value for idRegistry can be set to “unknown” if no common registry is used. This aspect has been a common factor leading to confusion and inconsistent implementations. 

Beyond the inconsistencies commonly seen in VAST4 implementations as outlined above, it’s important to note that the <UniversalAdID> element does not exist in VAST 2 or VAST 3 and has led to further confusion in the application of creative asset IDs. Historically, this has complicated the ability to accurately track individual creatives across platforms required for reporting, frequency capping, competitive separation, and server-side ad insertion (SSAI) caching. 


The purpose of this document is meant to serve as guidance to end the confusion around specifying a unique creative asset ID, and to homogenize the handling of <UniversalAdID> and <Creative> elements.


Moving forward, it is recommended that when sourcing VAST 4.x files, vendors should never use “unknown” as the value of the <UniversalAdID> element or its idRegistry attribute. Instead, in order of preference, vendors should:

  1. Use an authoritative program (such as the Ad-ID program in the United States, or Clearcast in the UK)
  2. Generate a UUID and use the canonical domain name of the vendor (i.e. ad server domain or any company that sources VAST files) as the idRegistry attribute.

=> If the <UniversalAdID> element is provided along with a valid idRegistry attribute, the unique creative asset ID should be constructed by concatenating:

  • the value of the  <UniversalAdID> element
  • a dot
  • the value of the idRegistry attribute


VAST file:
<UniversalAdId idRegistry=””>CNPA0484000H<UniversalAdId> 

Resulting ID:

=> If the approach above is not possible, use the Mezzanine URL to uniquely identify the asset. The unique creative asset ID would then be constructed by:

  • hashing the <Mezzanine> file URL using the MD5 function.

VAST 2 & 3

Because <UniversalAdID> and <Mezzanine> elements are not available in versions of VAST prior to 4.x the alternative approach for providing unique creative asset IDs is as follows.

=> If the <Creative> element is provided with both id and adID attributes, the unique creative asset ID should be constructed by concatenating:

  • the value of the adID attribute
  • a dot
  • the value of the id attribute


VAST file:
<Creative id=”120503″ adID=”119635032″> 

Resulting ID:

Barring the ability to use the above options (whether for a VAST 4, 3 or 2 tag), the first <MediaFile> element in the VAST file may be used.

=> The unique creative asset ID should then be constructed by:

  • hashing the first <MediaFile> URL using the MD5 function.

However, this has a limitation as the asset / URL needs to be static (no transient value like a timestamp) for this to work.

Although we are providing a method for VAST 2 and 3, it is our strong recommendation that companies upgrade to VAST 4.x for clean and clear identification of creative assets and several other improvements VAST 4.x provides.

If you have further questions, please contact, or visit our VAST specs page


Mike Midden
Director, Product Management
IAB Tech Lab