The next step in preserving supply quality: app-ads.txt

March 14, 2019

Tags: 2019, Industry Perspectives, Publishers, DSPs, Marketers

Samantha Solmonson
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Ad fraud comes in many forms. One such form involves unauthorized sellers falsifying the domain of a webpage, or the ID of a mobile app, to mimic another publisher’s legitimate site or app. The original ads.txt specification (“ads” stands for “Authorized Digital Sellers”) was developed by the IAB Tech Lab in the spring of 2017 to counter this type of fraud, and also to help publishers reign in the unauthorized reselling of their inventory, a practice that has become particularly rampant in the desktop/web environment.

How it works

The IAB has just released its final version of the app-ads.txt specification, which is an extension of the original ads.txt specification specifically for in-app inventory.

The spec itself is relatively simple. Publishers have the option to post their Authorized Digital Sellers Lists as app-ads.txt files to their developer web pages. The developers’ app store URLs are then passed to DSPs via bid requests, whereby DSPs may crawl the app store URLs for developers’ web pages and reference the published files to determine whether sellers are in fact listed as authorized.


During 2018, we saw ads.txt 1.0.1 achieve widespread adoption across the industry’s desktop/web inventory, with some brand marketers and DSPs only buying web inventory that has ads.txt implemented. This makes sense, given the high amounts of unauthorized reselling that occurs in desktop/web advertising, although this practice tends to be less common in mobile in-app.

So far we have seen a small, but growing, number of mobile app publishers implement the recent beta version of app-ads.txt. However, it has yet to be determined whether app-ads.txt will have the same adoption and effect on in-app as ads.txt has had on desktop/web.  

Looking ahead

Because MoPub’s SDK is integrated directly into our publisher partners’ apps, every bid request on our exchange is directly authorized by the publisher to be sold at auction by MoPub. That said, we understand the importance of helping our publishers protect their inventory and for DSPs to ensure the quality of their supply sources. Therefore we are in the process of determining how best to support app-ads.txt on our exchange. Ad fraud is an insidious threat to our industry as a whole, and we commend the efforts of those such as the IAB Tech Lab whose innovations and collaborative thinking help to preserve the quality and continued growth of our industry.

Update: On May 8, 2019, MoPub announced support for app-ads.txt. Learn more here.

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