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Tips, Tricks, and Best Practices for using Ads.txt

Tips, Tricks, and Best Practices for using Ads.txt

4 Minute read

Ads.txt is a great initiative. But, it's not living to its full potential.

Since the introduction of ads.txt in 2017, it has seen increasing adoption rates throughout the digital publishing and advertising communities. The main challenge of ads.txt is that once implemented, most publishers don't maintain it, don't validate new sellers' lines before adding them to the file, practically exposing themselves to fraud and malpractice.

This blog will go over what ads.txt is, how it works, and what best practices we've learned since it was created. (If you are already familiar with ads.txt, skip to the end for the best practices for managing your ads.txt file).

What is ads.txt

The Ads.txt initiative from the IAB Tech Lab aims to increase brand confidence in buying authentic publisher inventory and prevent internet ad fraud.

Ads.txt stands for Authorized Digital Sellers and is a simple, flexible, and secure way for publishers to publicly declare which companies they allow to sell their digital inventory. Its first version became available on June 27, 2017, and over 1.2M domains show the file.

Why implement ads.txt

When publishers implement ads.txt and advertisers require it, they help protect the industry from alleged domain spoofing attacks by fraudsters pretending to be the publisher's domain.

Domain spoofing is a technique used to trick buyers into purchasing masked sites instead of those the seller declares. In this case, an impostor site offers its inventory as if it was the actual site, leading programmatic buyers to purchase it instead of the legitimate inventory.

Ads.txt overcomes this problem by restricting the site to authorized sellers. Many buyers will blocklist publishers who do not implement ads.txt, as they want to make sure they are only purchasing authorized traffic.

As a result, the publisher controls its inventory in the market, ensuring that its impressions are not diluted by millions of spoofed impressions. As a side effect, the programmatic industry is being cleaned up.

How ads.txt works

The ads.txt mechanism represents a text (.txt) file that companies host on their web servers, listing the companies authorized to sell their ad inventory. As this text file is publicly accessible, programmatic buyers can index and reference it by crawling the web for ads.txt files before purchasing inventory on open markets. Buyers can match the retrieved data against the bid request and make their purchasing decisions accordingly, filtering out unauthorized sellers.

The buyer receiving a bid request claiming to be can check to see if the seller account id and exchange match the listing in

These are the definitions of the fields in an ads.txt line:

Introducing App-ads.txt and support of CTV

To improve app inventory transparency, the IAB Tech Lab released an extension to the ads.txt initiative customized for apps, called App-ads.txt, released in 2018. The app version of ads.txt also supports OTT and CTV, allowing publishers to list the vendors authorized to sell their ad inventory. CTV growth is booming; however, the high CPMs attract ad fraud, and complexities of monetization relationships such as "inventory sharing" make it harder for current ads.txt and app-ads.txt specifications to provide enough transparency. So, the IAB Tech Lab has recently been working on enhancing CTV standards that offer improvements.

Best Practices for ads.txt implementation and maintenance

The IAB publishes the most updated specifications of how to implement ads.txt files. We recommend checking their website before implementing your ads.txt file.

Once the file is set up, you'll add the ads.txt lines from your sellers. The ads.txt file directly impacts your monetization, so you must validate the lines before adding them to your file.

Here are the five most important things you should keep in mind:

1. Invalid lines are useless. Stick to the exact IAB format. Make sure to use the precise number of spaces and commas.

2. Cross reference ads.txt and sellers.json to discover the sellers behind the lines. You can use's "Validate Ads.txt" feature for that.

3. Own your domain. You are the only seller that needs to be listed as DIRECT in your file.

4. Clean up. Remove lines of partners you are no longer working with.

5. Run overall quarterly checks. Make sure there are no loopholes.

If you have any questions or suggestions for more best practices, feel free to contact us.

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