Mozilla commissions CheckFirst to conduct a stress test of Ad Repositories
First comprehensive report on DSA-strengthened platform ad libraries, finding the ad transparency tools failing to meet their intended purpose.
Executive summary
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Commissioned by Mozilla, CheckFirst stress-tested the ad repositories of 11 major platforms — including Meta, Google (Search and YouTube), TikTok, X, LinkedIn, Snapchat, Pinterest, Bing, AliExpress, Booking.com, and Zalando — against more than 20 criteria drawn from Digital Services Act transparency requirements and Mozilla's earlier Ad API guidelines, assessing functionality, data accessibility, and accuracy.
None of the repositories fully met the baseline criteria. Only 5 of 14 tools examined were reachable directly from the platform's main interface, and researchers documented recurring problems such as weak search, filtering and sorting capabilities, inconsistent data formats, missing ads, and inadequate disclosure of influencer content. X's repository was singled out as especially poor, offering no filtering or sorting and requiring a CSV export just to view ads.
The report concludes that current ad transparency tools fail to serve their intended purpose of enabling researchers to monitor disinformation, scams, and election-law violations, and recommends adopting a standardized, interoperable advertising-disclosure format across platforms.
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