Ads.txt and How it can Save Companies Millions of Dollars

Wherever there is an opportunity for a person to make a lot of honest money; unfortunately, there will usually be those looking to take advantage of that same opportunity in nefarious ways. With advertising being an industry that spends hundreds of billions of dollars every year, there is not a shortage of those shifty characters waiting to take advantage. Luckily advertisers are not defenseless against scams and attacks; this is where ads.txt comes in.

What is Ads.txt?

Simply put, ads.txt is just a list of organizations you can trust when purchasing ad space, with ads standing for Authorized Digital Sellers and .txt showing that it is a text file. This list was released in 2017 by the International Advertising Bureau (IAB) to help protect against malicious actions, including:

  • Inventory arbitrage – the buying and reselling of ad space for a higher price
  • Domain spoofing – the act of changing a legitimate URL for a fraudulent URL, typically done by malware or by the bad actor making manual changes to the ad.

How Ads.txt Works

Ads.txt contains information in these fields:

  • Publisher’s Account ID.
  • The advertising system’s domain name.
  • Whether the account is DIRECT or a RESELLER, with the former being a publisher selling their inventory directly and the latter being a separate company with permission to sell ad inventory.
  • Certification Authority ID, this is entirely optional and shows if a vendor is authorized by a third party.

Publishers and programmatic sellers place this file in the root of their web servers, allowing inventory sellers and ad space to be validated. This prevents fraudulent sellers from buying inventory to resell at a higher price, as well as preventing them from selling ad space that is not available.

Does Ads.txt Work with Mobile Devices?

It didn’t seem original when the IAB released ads.txt in 2017, as the app stores for mobile devices did not support it. Due to this, the IAB worked with ad tech companies and app stores to tweak the format of ads txt for apps. This ran into a hurdle, however, due to the fundamental difference between how web browsers and apps store their files.

To address this technical problem, an extension was released called app-ads.txt that addresses the technical requirements for this approach to ad security in app form.  This allows an app ads txt to function for both mobile and connected TV (CTV) devices.

How to Best Use Ads.txt

The first step is to have an ads.txt file, to begin with, there are some best practice techniques to get the most out of this line of defense:

Check for Errors

Something as simple as incorrect syntax or typoes can prevent those interested in your inventory from being able to scan the file correctly. This potentially leads to your inventory being ignored, which directly reduces revenue.

Cover your Bases

Ads.txt is a great first defense against ad fraud, but a truly robust defense requires more than just a single tool. This can be a service provided by fraud detection companies, which have tools that can check whether or not ads are being displayed in the correct ad space, the right app, or website. 

Keep it Short

The longer the list, the larger the ads.txt file will become, and this can be problematic for demand platforms to process. Large files can lead to lists not being fully read by systems or even ignored entirely. If the list is completely ignored, then ads can be banned from an entire domain, which would lead to a significant drop in income. Because of these potential problems that can arise from file size, it’s best practice to strictly review any additions or new entries to the ads.txt file to make sure that the changes are appropriate and worth the size increase.


To avoid fraud, certain best practices should be employed, such as using ads.txt, app ads.txt, and other tools to verify programmatic sales. With the increasing value of the ad industry and the growth of ad space as people rely more and more on technology, companies would be wise to safeguard their valuable ad inventory and budgets.

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