There was an unexpected error authorizing you. Please try again.

IAB Tech Lab Aims to Increase Transparency Across Entire Advertising Supply Chain For New ID Usage

The Rearc Accountability Working Group Releases id-sources.json for Public Comment 

NEW YORK, NY –  October 13, 2021 – As the advertising ecosystem readies itself for a post-cookie world, it is not readily clear which companies are adopting the various new user ID solutions. To help increase transparency around ID solution usage, IAB Tech Lab, the digital advertising technical standards-setting body, today released id-sources.json. The standard will be available for public comment until November 12. 

id-sources.json was developed out of the Rearc Accountability Working Group to enable companies to declare the user identity sources they use. This first-of-its-kind transparency results in a range of benefits across the ads ecosystem. Among those benefits, brands, agencies, and publishers who are integrated with identifiers from different providers can quickly recognize the supply paths in which they can activate addressable audiences.  

“It’s critical that companies integrating with user identity sources do so in the open if they hope for this rapidly growing infrastructure to be sustainable in the face of privacy-driven changes,” said Alex Cone, Vice President, Privacy & Data Protection, IAB Tech Lab. “We believe this is a foundational step toward accountability solutions that enable new forms of addressability to thrive in a post-third party cookie world  and is in line with IAB Tech Lab’s commitment to improve industry transparency.” 

id-sources.json aims to: 

  • Provide a standard way for companies to declare which user identity sources they use
  • Work like the other IAB Tech Lab supply chain transparency standards (e.g. sellers.json and buyers.json). It is a participant hosted, structured declaration that machines can read
  • Ease ad campaign execution between advertisers, publishers, and their chosen technology providers by making it clear who supports what ​​

“As companies turn to different identity solutions that will replace the role of the third-party cookie, it’s important we continue to push for a transparent supply chain,” said Caitlin Fitzharris, Senior Product Manager, Index Exchange. “Knowing which identifier is used by whom helps all parties, and id-sources.json is an important step towards building auditable data structures to ensure consumer privacy.”

To review the proposed standard and provide feedback, please go to: and visit

About IAB Technology Laboratory

Established in 2014, the IAB Technology Laboratory (Tech Lab) is a non-profit consortium that engages a member community globally to develop foundational technology and standards that enable growth and trust in the digital media ecosystem. Comprised of digital publishers, ad technology firms, agencies, marketers, and other member companies, IAB Tech Lab focuses on solutions for brand safety and ad fraud; identity, data, and consumer privacy; ad experiences and measurement; and programmatic effectiveness. Its work includes the OpenRTB real-time bidding protocol, ads.txt anti-fraud specification, Open Measurement SDK for viewability and verification, VAST video specification, and Project Rearc initiative for privacy-centric addressability. Board members/companies are listed at For more information, please visit

IAB Tech Lab Media Contacts
Kate Tumino / Brittany Tibaldi
212-896-1252 / 347-487-6794 /