Full Disclosure: Stress testing tech platforms’ ad repositories

April 16, 2024
Ads transparency / Elections


The ad libraries provided by large tech platforms are designed to give insight into the role of advertising and paid influence on services which are used by billions every day. These libraries collect ad content (the ads people see) and information about the intention of ad campaigns, giving researchers and the public a view into how commercial communications are used to influence the information space.

The EU Digital Services Act (DSA) regulation requires that the largest online platforms and search engines (those designated by the EU Commission as “Very Large Online Platforms and Search Engines") have public ad libraries. This harmonized legislative requirement is welcome and doesn't come a moment too soon, with elections taking place in the EU and around the world.

The effectiveness of these tools depends on their usefulness for researchers in practice. In this independent “stress test”, we assessed whether the available ad repositories are ready for action. We examined the following services: AliExpress, Apple App Store, Bing, Booking.com, Alphabet (Google Search and YouTube), LinkedIn, Meta (Facebook and Instagram), Pinterest, Snapchat, TikTok, X, and Zalando.

These tests aimed to uncover any potential inefficiencies or shortcomings in the ad repositories and identify areas for improvement for real world use. Stress testing was used to evaluate the robustness, reliability, and effectiveness of the ad repositories under various conditions and loads, to mimic real-world demands and challenges. Meanwhile, usability testing aimed to ensure that the ad repositories are also user-centric, since a system can be technically sound, but if it's not user-friendly, its effectiveness is limited.

We find approaches to ad transparency vary widely among the platforms studied. While these tools are far from perfect, we applaud these companies for getting this far, and we make several recommendations that we hope can be useful for their continued improvement.

We encourage you to test them out yourself! You can find the web repositories and APIs below.

Ad Repository Links




Apple App Store









X (Twitter)