ads.txt

The dominant open industry standard for publisher inventory authorization, maintained by IAB Tech Lab and adopted by millions of publisher domains globally.

ads.txt (Authorized Digital Sellers) is an IAB Tech Lab initiative launched in 2017 that allows digital publishers to publicly declare the companies authorized to sell their digital advertising inventory. The standard works by having publishers place a simple text file at the root of their domain listing all authorized sellers, which buyers and DSPs can then crawl to verify that impressions are being sold through legitimate channels. This transparency mechanism directly combats domain spoofing and unauthorized reselling, two of the most prevalent forms of ad fraud in programmatic advertising. The standard has seen widespread adoption across the digital advertising ecosystem, with millions of publisher domains implementing ads.txt files. Complementary standards have since been developed, including app-ads.txt for mobile and CTV app inventory, and sellers.json which provides the supply-side counterpart by requiring SSPs and exchanges to disclose their seller relationships. Together these standards form a critical layer of supply chain transparency in programmatic advertising. ads.txt is not a company but an open technical standard maintained by the IAB Tech Lab, a nonprofit research and development consortium. It requires no licensing fees and is freely implementable by any publisher or buyer. The standard is enforced through buyer-side adoption — DSPs and advertisers check ads.txt files before bidding, creating market incentives for compliance. Its significance in the AdTech ecosystem is substantial, as it has become a baseline requirement for brand safety and supply chain integrity across major programmatic platforms.