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While fraud in the digital ecosystem comes in various forms, ads.txt is the latest initiative from the IAB that specifically focuses on preventing the sale of counterfeit inventory. Ads.txt accomplishes this by providing a means for buyers to authenticate inventory is coming from an authorized seller during the real-time bidding process. In our last Product Pulse, we explained what ads.txt is and why SpotX supports it. In today’s Product Pulse we’ll take a closer look at how ads.txt works.

An ads.txt file is hosted on a publisher’s domain and includes a list of all authorized sellers. Because the ads.txt file is hosted on the the publisher’s domain, it authenticates the information as only the domain owner has the ability to add sellers to this file and post it to their site.

What’s included in an ads.txt file?

An ads.txt file contains a line for each authorized seller and each line includes up to four fields:  

Field Name Description
Field #1 Domain name of the advertising system This field identifies the advertising system, like an SSP or exchange, that the buyers connect to.
Field #2 Publisher’s account ID This field includes the identifier associated with the seller or reseller account within the advertising system listed in field #1.
Field #3 Type of account/relationship This field indicates whether the inventory is being sold direct by the owner or through a reseller.

‘DIRECT’ indicates that the publisher (content owner) directly controls the account indicated in field #2 on the system in field #1.

‘RESELLER’ indicates that the publisher has authorized another entity to control the account indicated in field #2 and resell their ad space via the system in field #1.

Field #4 Certification authority ID The current certification authority used is the Trustworthy Accountability Group (TAG). This field should list the TAGID that uniquely identifies the advertising system, named in field #1.

To illustrate the contents of an ads.txt file, let’s use, a fictional publisher as an example. uses SpotX as their SSP and sells their inventory through SpotX.’s publisher ID in SpotX is 123456 and SpotX’s TAGID is 7842df1d2fe2db34. would host their ads.txt file at and the file would include the following information:

#Ads.txt, 123456, DIRECT, 7842df1d2fe2db34

Now let’s expand on this example by adding an instance of a reseller. outsources the sale of their European inventory to Company A. Company A also uses SpotX to sell their inventory on and their Publisher ID in SpotX is 7891011. would add a line to their ads.txt file hosted at to include Company A as an authorized seller through SpotX:

#Ads.txt, 123456, DIRECT, 7842df1d2fe2db34, 7891011, RESELLER, 7842df1d2fe2db34 would add an additional line item for each advertising system they sell through and for all resellers they authorize to sell their inventory.

How do buyers use ads.txt to verify authorized sellers?

Buyers can crawl the web to generate a record of all Authorized Digital Sellers for every domain they wish to purchase inventory from. When a buyer receives an ORTB bid request from inventory on one of these domains, they are able to verify the sale using the information contained in the domain’s ads.txt file.

To do this, the buyer would check that the ORTB bid request is coming from the advertising system listed in field #1 of the ads.txt file and that the publisher ID listed in field #2 of the ads.txt file is included in the ID field of the publisher object. If both of these fields are included in the bid request, the buyer can be assured they are purchasing legitimate inventory from an authorized seller.

The success of ads.txt is contingent upon adoption by both buyers and sellers and SpotX strongly encourages all of its publishers to implement ads.txt on their domains.  Now that you know what ads.txt is and how it works, visit the SpotX Developer Center to learn how to implement ads.txt today.

Screen Shot 2017-10-04 at 3.11.58 PMInsights from:

Amanda O’Hara, Manager, Product Marketing





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