Online advertising is a multi-billion dollar industry that places hundreds of millions of adverts on tens of millions of web pages every day. For good and for bad, advertising is the engine of the online economy, but few consumers are aware of the incredible complexity of the system that chooses which adverts they see. That system is far from perfect, and one of its biggest problems is fraud.
When an advertiser decides to buy advertising space on a web page, how do they know that their advertising ends up where they expect it to? Historically, there has been no way for them to be sure, a loophole that is exploited by fraudsters.
Ads.txt – “ads” stands for authorized digital sellers – is an initiative from the Interactive Advertising Bureau that aims to stop one type of fraud by giving publishers a way to declare who is authorized to sell advertising on their pages.
Put yourself in the position of an advertiser. You have a product to sell and you want to promote it on the pages of a high-profile publication. The publisher would love to have your business and the money that comes along with it. An advertising network that you work with says it can sell space on the publisher’s pages, and so you pay a premium rate to get your product in front of the right people.
Except the advertising network isn’t really selling space on your preferred publisher. They’ve been tricked by a criminal who is actually selling advertising on a low-traffic, and possibly distasteful, site. You’re paying top dollar to place advertising on a site where hardly anyone will see it, and your advertising dollars are going to a fraudster rather than a legitimate publisher.
Ads.txt is a file that publishers upload to their sites. The file contains their publisher ID and a list of the supply side exchanges who are authorized to sell the advertising space. Demand-side advertising networks can crawl ads.txt files to build a list of the networks and exchanges that are authorized to sell advertising for that domain. The fraudsters can’t sell their bogus stock because the buyers know they don’t have the necessary authorization.
Ads.txt is supported by most of the largest advertising networks, and many of the most prominent publishers on the web have seen increases in advertising revenue because less money is being funneled away by fraud.

Ads.txt On WordPress

To benefit from the ads.txt system, publishers must upload an ads.txt file to the root domain of their site. The ads.txt file follows a format described in the official specification from IAB. Uploading an inaccurate ads.txt file might negatively impact advertising revenue, so it’s worth taking the time to familiarize yourself with the specification and this less comprehensive guide.
Web development agency 10up has created a WordPress plugin that allows site owners to create and validate their ads.txt file from within the WordPress dashboard.