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Tags: Programmatic, Publisher, IAB, Ad Serving

Updated: March 11, 2021

Authorized Digital Sellers or ads.txt is a project launched by IAB Tech Lab in 2017 to help ensure that digital advertising inventory is sold only through vendors designated by the publisher as authorized sellers. The Ads.txt file is like a public register of authorized partners on the site. It allows you to manage your inventory sales and prevent fraud. Ads.txt has been a standard for several years and is widely used by publishers.


How does ads.txt work?

In practice, publishers add a text file to the site that lists all the platforms that are allowed to sell the publisher’s inventory. The Ads.txt file is uploaded to the root of the site ( Once the file is loaded correctly, you will be able to see the contents of the file when you add the /ads.txt extension after the domain. The file allows buyers to verify the accuracy of the ad inventory they purchase and to verify that the file ID is the same as in the purchase platform. In addition, the buyer can also look at the publisher's website from which platforms it is possible to purchase that publisher's inventory.

Installing and updating the file requires a bit of work, but in practice it is quite simple.


Here's how to compile and add ads.txt to your site

First, you need to create a text file, name it ads.txt, and save each of your partners in it. Each partner has its own line, and each line must contain three mandatory comma-separated information and one optional:


  1. The domain of the ad platform you are using, e.g.
  2. Your website ID in the platform, i.e. publisher ID or network ID. Note! This tag is different for each publisher.
  3. Information about the type of partnership either “Direct” or “Reseller”. If the site owner manages / maintains the sales platform itself, the type DIRECT is used, while if the authorized platform is managed by someone else (reseller), the type RESELLER is used.
  4. The TAG certification ID is the certification ID for that system. For example, the ID is f08c47fec0942fa0. The TAG certificate field is optional and can be omitted if the partner does not have one.


Single direct Ads.txt entry:

One directly authorized system managed / maintained by the website owner:, pub-XXXXXXXXXXX, DIRECT


One authorized system maintained by a company that resells publisher inventory:, XXXXX, RESELLER


Multiple authorized systems and multiple resellers. Some of their authorized systems are certified, so a TAG certificate identifier has been added as the fourth information:, pub-XXXXXXXXXXX, DIRECT, f08c47fec0942fa0, XXXXX, RESELLER, 12345, DIRECT, 5d62403b186f2ace


Once you have created a list of all your partners, you need to save the file and add it to the root folder of the website. Please note that you cannot copy data from another publisher's file, but the ads.txt file must include the publisher's own partners and their own IDs.


Validating the Ads.txt file

Ads.txt is only useful if it is done and saved correctly. For this reason, it is a good idea to make sure there are no errors in the list. There are validators for the review. Entering the ads.txt URL into the validator verifies that the information is in the correct format and that the publisher / Network IDs actually exist. You can easily find validators by Google (e.g.


What about App-ads.txt?

App-ads.txt is an extension of the original project for mobile in-app and OTT advertising. The file is created in the same way as Ads.txt, but is named app-ads.txt. Partners are added to the app-ads.txt file in the same way as ads.txt, but the challenge with publishing is that the app does not have a domain where the file could be published. However, app-ads.txt files should be publicly available and indexable. Alternatively, you can add the Developer domain of the app to the app developer information on Google Play and the App Store and upload the file to the root of that domain, or use a separate hosting service to add the file.


Why is ads.txt important for publishers?

Ads.txt benefits the entire digital market. It can help prevent fraud and increase the reliability of programmatic purchasing of advertising. In addition, it allows you to prove that your website and partners are trustworthy and thus increase the commercial value of your site. In addition, many Demand side platforms (DSPs) allow purchasing of ad inventory only from the pages that contain an ads.txt file. That is, if the file is not found on the page, it excludes potential buyers of advertising and thus negatively affects advertising revenue. In addition to reliability, you can also use Ads.txt to market to an advertiser where you can purchase your inventory.

Remember to keep your ads.txt file up-to-date and update it if there will be more partners or someone's representation ends. Otherwise, there is no need to maintain the file. To enjoy the benefits of ads.txt, keep in mind: keep your Ads.txt file error-free, up-to-date, and only with the needed information.

Suvi Leino
By: Suvi Leino

Responsible for marketing and communications at Relevant Digital.


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