app-ads.txt

The dominant open standard for authorized seller declaration in mobile app and CTV advertising, maintained by IAB Tech Lab and broadly adopted across the programmatic ecosystem.

app-ads.txt is an IAB Tech Lab initiative launched in 2019 as an extension of the original ads.txt standard to address the unique challenges of mobile app and connected TV (CTV) advertising ecosystems. Unlike web-based ads.txt files hosted on a domain, app-ads.txt files are hosted on the developer's website registered in the app store, allowing buyers and verification systems to crawl and validate authorized sellers for a given app's inventory. The standard was created to combat ad fraud, unauthorized reselling, and domain spoofing in in-app and CTV environments. The specification works by requiring app developers to publish a plain-text file on their developer website that lists all authorized supply-side platforms (SSPs), exchanges, and resellers permitted to sell their ad inventory. Demand-side platforms (DSPs), advertisers, and verification vendors then crawl these files to validate that impressions being offered in bid requests come from legitimate, authorized sources. This creates a transparent, publicly auditable chain of authorized sellers. app-ads.txt has become a foundational fraud-prevention and supply chain transparency tool in the programmatic advertising ecosystem. It is maintained by the IAB Tech Lab as an open standard and is widely adopted across major SSPs, DSPs, app stores, and measurement vendors. Its adoption is considered a best practice for brand safety and supply path optimization (SPO), and it complements related standards such as sellers.json and OpenRTB.