It aims not only at increasing transparency and trust of the supply chain, but also at guaranteeing a quality of inventory to the demand side who will be more likely to buy.
Sellers.json is an IAB provided standard that provides a mechanism to enable buyers to discover who the entities are that are either direct sellers of or intermediaries in the selling of digital advertising.
A published and accessible sellers.json file allows the identity of the final seller of a bid request to be discovered (assuming that they are ads.txt authorized).
It also allows the identities of all nodes (entities that participated in the bid request) in the Supply Chain object to also be discovered.
Currently, it is possible for the final seller to be identified via the Publisher.name and Publisher.domain attributes, but in practice, these properties are inconsistently populated by various selling systems.
Sellers.json enables smaller bid request object sizes by allowing this information to be looked up and cached “offline” rather than supplied with every bid request. Sellers.json also allows the identification of any and all intermediaries that participated in the selling of a bid request.
Definition provided by IAB Tech Lab
The objective of Sellers.json is to avoid ad fraud, as it allows buyers to see direct sellers and intermediates selling programmatic ad inventories.
It aims not only at increasing transparency and trust of the supply chain, but also at guaranteeing a quality of inventory to the demand side who will be more likely to buy.
To give you a clearer idea, here is how Opti Digital Sellers.json looks like