Breaking Down Ads.txt

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Ads.txt (where ADS stands for Authorized Digital Sellers) is an adopted standard across ad tech for publishers and advertisers to combat a type of ad fraud known as “domain spoofing”. This ad fraud is perpetrated by the sell-side (SSPs and exchanges) against the buy-side (DSPs and advertisers) where they are selling fraudulent impressions instead of having legitimate impressions. We want to be clear that it is not publishers such as yourself committing the fraud — rather it is unscrupulous actors pretending to represent you.  Publishers are indirectly impacted by this ad fraud because the advertiser purchases fraudulent impressions and thus, that ad spend is redirected to a fake impression. It was only in the spring of 2017 that the Interactive Advertising Bureau (IAB) Tech Lab introduced ads.txt as a tool to help buyers avoid buying counterfeit inventory. 

How Does Ads.txt Work?

As a publisher, you add a text file to your web server that lists all of the SSPs and exchanges that are authorized to sell your inventory. Any website can use an ads.txt file as long as it contains the correct information and lives on your domain as “”. The ads.txt file includes the following information as outlined by the IAB:

  • Domain name of the SSPs and exchanges (ex.
  • Account ID (ex. 4052)
  • Type of relationship (ex. reseller)
  • TAGID (ex. f08c47fec0942fa0) – Optional
  • Notes – Optional; Robots crawling your ads.txt file will ignore anything after the “#”

Buying platforms (DSPs and advertisers) crawl the web to acquire the ads.txt file for every domain. The ads.txt file gives the buyer the ability to check if an impression is legitimate by verifying if the SSP is authorized to sell your inventory, and that the account is actually yours. This allows the buyer to detect if the SSP is telling them false information about their ability to sell the impression and helps the buyer avoid purchasing counterfeit inventory. This is helpful when fighting back against domain spoofing attacks where fake websites clone popular sites and try to sell their ad space. 

You may be wondering what the difference is between a Direct or Reseller line. It’s fairly self-explanatory. A direct line means the publisher is selling directly with the SSP or exchange, whereas a reseller means the publisher authorizes the SSP or exchange to resell their ad inventory to another SSP or exchange.

To give you an idea of how websites use it, here two few examples of ads.txt files:

Why Does this Matter?

The issue that ads.txt tackles is ad fraud. It protects the buy side from purchasing counterfeit inventory and verifies that the SSP is authorized to sell the inventory – preventing counterfeit inventory from being purchased. Prior to ads.txt, unless buyers are working directly with publishers, there was no way of knowing which SSPs were authorized to sell a particular publisher’s inventory. Ads.txt helps address this problem by giving buyers the choice to only buy from authorized digital sellers of a participating domain. Ads.txt alleviates this issue for the whole programmatic ecosystem. 

  • Publishers are able to reclaim control of their media and brand. This means more of an advertiser’s spend can get to you through your approved sales channels, and not be wasted on counterfeit inventory.
  • DSPs and advertisers can be more confident that their working media budget is going to accountable media and not counterfeit inventory.

Source: IAB Tech Lab

Many publishers turn to programmatic advertising to help monetize their website(s). Ads.txt provides a safety net for buyers in protecting them from purchasing counterfeit inventory. It allows buyers to buy with more confidence – buyers may choose not to buy from your site if they can’t verify if the SSP is authorized to sell your inventory. 

What are the Benefits of Ads.txt for Publishers?

Fraud continues to permeate online activities with businesses losing billions of dollars. Using ads.txt helps prevent fraudsters from impacting the programmatic advertising ecosystem, and it starts with you, the publisher, taking a stand against ad fraud by adding an ads.txt file to your site. Here are just a few of the most significant benefits to a publisher:

  • Access to more SSPs and exchanges – You need an ads.txt file to enable SSPs and exchanges to bid on your inventory. By having more available bidders, you can increase competition and in return, have a positive impact on your ad revenue. 
  • Easy to install The file is incredibly easy to install on your website(s). Copy the file over to your root domain (
  • Easy to edit – You can quickly and easily update your ads.txt files by simply editing that file. This means if you need to add new sellers to the list, you can do that with minimal effort.
  • Protects you from unauthorized sellers – It gives buyers a way to check if the inventory is fake or not. Buyers who want to advertise on your domain will be able to do so, with less chance of their spend being diverted to a fake version of your account. 

What are the Drawbacks of Ads.txt for Publishers?

You need to allocate a web developer or an Ad Ops specialist to integrate these text files and monitor them whenever you or your Ad Ops partner adds additional SSPs and exchanges. We recommend doing a monthly check to ensure they’re up to date.

Ads.txt may not be a high priority for you. That’s why several Ad Ops developed hosted ads.txt, a cost-free way for you to control and manage your own ads.txt file while they host it for you. Add your custom ads.txt lines to the Ads.txt page (expand Site Settings in the left navigation menu) and when our ads.txt page is updated, your ads.txt page is automatically updated too. You don’t have to manually update your page every time they update their file (aka, whenever they add new bidders) and you don’t have to pay a cent. Once your custom lines are in, you’re off to the races!

As you can see from above, the ads.txt file makes a difference to programmatic advertising to combat ad fraud and plays an integral part in the Ad Ops landscape. Publishers have the opportunity to help by installing ads.txt and keeping them up to date. 

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