At its most basic level, it is a text file that contains lines of code. At its most sophisticated level, it is a secure, flexible way for publishers to allow approved companies to sell their digital advertising inventory.
You might assume that the “ads” in ads.txt is referring to advertising, but it’s actually an acronym for Authorized Digital Sellers. It’s a project from the IAB Tech Lab that, shortly after its release, gained widespread adoption and even became a featured part of Google AdSense’s user interface.
Programmatic advertising can happen on a wide variety of channels, and because each of these channels is susceptible to ad fraud in unique ways, ads.txt has grown to include not just websites, but apps and over-the-top (OTT) platforms.
Ads.txt for Web
Ads.txt started with websites. For web publishers, ads.txt is a text file that the publisher creates and hosts on their site, usually at a top-level URL that looks something like this:
That text file contains information that authorizes particular exchanges and supply-side platforms (SSPs), or sellers, to sell the publisher’s traffic. When buyers are responding to bid requests, they verify that the seller is listed in the publisher’s ads.txt file to ensure that the transaction is safe and fraud-free.
A couple of years after ads.txt was created, the IAB Tech Lab saw the need for a similar fraud-prevention solution in the in-app advertising space. Apps may be distributed via relatively secure app stores, but they are just as vulnerable to ad fraud as websites.
That realization led to the creation of app-ads.txt. It does basically the same thing as ads.txt, but it’s specifically meant for apps. Keep in mind that, while ads.txt and app-ads.txt do essentially the same thing but for different channels, they are separate files that authorize different sets of sellers.
As OTT advertising has grown in tandem with sales of Rokus and similar devices, ad fraud has also grown in this space. Ad tech industry leaders didn’t have to engineer a whole new solution for this problem, though. They already designed app-ads.txt for use in OTT channels.