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All you need to know about ads.txt and sellers.json files

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In the evolving landscape of programmatic advertising, numerous industry initiatives have emerged to tackle challenges related to transparency, fraud prevention, and trust. Among them, the implementation of ads.txt and sellers.json files, widely adopted by the online publishing industry. In this article, we’ll look at how to implement them and what their main benefits are.

I- What is Ads.txt and how to implement it correctly?

a) Purpose and origin of the ads.txt file

Ads.txt, which stands for Authorized Digital Sellers, is an initiative set up by the IAB Tech Lab, to enable publishers to publicly declare which sellers are authorized to sell their digital ad inventory. By declaring only trusted partners in this file, publishers ensure that advertisers are not offered fraudulent inventory. In the ads.txt file, sellers are identified by their unique seller account ID, so advertisers can cross-reference the sellers account IDs listed in the ads.txt file with the sellers they want to work with. This way, advertisers can ensure that the sellers they engage with are authorized by the publisher. 

Although implementation of this file is not mandatory, it is strongly recommended that online media publishers implement it, as it is proven to attract more advertisers. In addition to promoting transparency and trust and limiting ad fraud, this information helps buyers understand the shortest path to directly access the publisher’s inventory without intermediaries.

b) How to set up your Ads.txt file?

Publishers can create an ads.txt file, using simple tools such as Notepad, or TexExit, before uploading it directly to the root directory of their site. Each row corresponds to one seller and is made up of a series of specific items of information, which is essential for identifying the seller.

SSP, Publisher ID, Account ID, Certification Authority ID

ads.txt file
Extract of an ads.txt file from a publisher working with Opti Digital 

To ensure that their ads.txt file is correctly implemented, publishers can add at the end of their domain “/ads.txt” ( The browser should display the content of the ads.txt file, showing the authorized sellers and their details. We also recommend that publishers check their files for syntax errors, for this several tools are available on the market, like Ads.txt Guru or We also advise publishers to periodically review their Ads.txt file to ensure it remains up to date and free from unauthorized entries. 

Additionally, due to the regular changes in the industry, the ads.txt file is frequently updated. Since April, the latest addition is the possibility to further clarify the relationship between publishers and demand partners. There are two new additional fields in the list: MANAGERDOMAIN, which specifies the entity managing the inventory on behalf of the publisher, and OWNERDOMAIN, which specifies the entity that owns the domain.

Maintaining an accurate and clean Ads.txt file is crucial for ad fraud prevention, building trust with ad buyers and also for not missing any demand. At Opti Digital, we automatically perform a daily check of the ads.txt file on publishers’ sites, comparing the file published to make sure it matches the list of demand partners connected to the media. We can then identify sites with missing lines or no ads.txt file, and contact the publisher directly to ensure that their site is optimized to attract the highest volume of demand.

II – Got a clean Ads.txt file? Check your partners’ sellers.json

a) What is sellers.json?

Sellers.json is a file that works hand in hand with the Ads.txt initiative. While Ads.txt is a publisher focused initiative that proves the legitimacy of sellers, sellers.json is for SSPs and provides crucial information about the intermediaries or resellers involved in the ad transaction process. It allows buyers to understand who is selling the ad inventory and which entities are involved in the supply chain, as well as the money transaction.

This file is typically hosted on the domain of the AdTech partner working as a SSP or as an intermediate doing the mediation between SSPs and publishers. Sellers.json file contains valuable information about each entity in the supply chain, such as their name, domain name, and the relationship they have with the publisher or seller. This information empowers buyers to make informed decisions when purchasing ad inventory, as they can verify the legitimacy of sellers and their relationships with publishers.

b) What information should appear in this file?

To ensure that your sellers.json file is readable and correctly configured, you need to fill in certain specific fields:

  • Seller_type: Usually publisher, intermediary, or both.
  • Seller_id: It is normally the same unique ID that the SSP should provide to the publishers for the ads.txt file.
  • Name: The legal name of the seller or the entity involved in selling the ad inventory.
  • Domain: The business domain name. It provides information about the digital property or platform used for selling ad inventory.

Here’s an example:


 “seller_id” : “p185”,

 “name” : “”,

 “domain” : “”,

 “seller_type” : “PUBLISHER”,

 “is_confidential” : 0


Working with publishers who possess a clean ads.txt file is just as crucial as collaborating with SSPs that maintain a sellers.json file. Indeed, working with supply-side platforms (SSPs) that have sellers.json files helps prevent ad fraud, improves transparency and, above all, enhances brand safety.

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files ads.txt & sellers.json
Source: Smart Hub

In conclusion, Ads.txt and sellers.json are powerful tools in promoting transparency in the programmatic advertising industry.

Ads.txt provides a means for publishers to declare authorized sellers of their ad inventory, ensuring that advertisers can confidently invest in legitimate placements. Sellers.json, on the other hand, complements Ads.txt by providing valuable information about the intermediaries or resellers involved in the supply chain. 

Thanks to these files, publishers and buyers can make informed decisions, mitigatsxse risks, and build stronger relationships based on trust and accountability. With the ongoing commitment to transparency and standardization, the programmatic advertising industry can continue to evolve in a more secure and reliable manner, benefitting all stakeholders involved.

To find out more about Opti Digital and the advertising technologies we offer publishers, contact our team of experts.

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