Sellers.json

Sellers.json is a public file, published by advertising exchanges and other intermediaries under a standard from the IAB Tech Lab (the technical arm of the Interactive Advertising Bureau), that declares the identities of the sellers and resellers authorized to offer digital advertising inventory through that intermediary. Any buyer can fetch the file at a well-known location and see, in the open, exactly which companies are permitted to sell a given publisher's inventory and whether each is the publisher itself or a reseller. It is part of a set of transparency standards built to fight fraud and opacity in the programmatic advertising supply chain, where inventory can pass through many hands between a website and the advertiser who ultimately pays for the impression. Sellers.json puts names to those hands.

The purpose is supply-chain transparency and trust. In an opaque market, an advertiser buying an impression cannot easily tell who actually sold it or how many undisclosed middlemen took a cut, which creates room for arbitrage, misrepresentation, and fraud. Sellers.json, together with the companion SupplyChain object passed in each bid request, lets a buyer trace an impression back through every authorized seller to its origin. If a seller appears in a bid but not in the relevant sellers.json file, that is a red flag that the inventory may be misrepresented. The standard does not by itself stop fraud, but it makes the supply path legible, so buyers can choose to transact only through disclosed, authorized sellers and hold the market to a higher standard of honesty.

Sellers.json is easiest to understand alongside its companion standards, ads.txt and app-ads.txt, because they solve the same fraud problem from opposite ends of the transaction. Ads.txt is a file a publisher hosts on its own website to list the sellers authorized to sell its inventory, the publisher declaring which companies may sell its ad space. App-ads.txt is the same idea for mobile apps and connected-TV apps. Sellers.json is the mirror image, published by the intermediary rather than the publisher: it declares which sellers the intermediary represents and their real identities. Together, ads.txt names who may sell from the publisher's side, and sellers.json names who those sellers actually are from the exchange's side, so a buyer can cross-check both and confirm the whole chain lines up.

The SupplyChain object completes the picture. Where ads.txt and sellers.json are static files declaring authorization and identity, the SupplyChain object is passed dynamically inside each bid request, listing every intermediary the impression actually passed through on its way to the buyer. A buyer can then verify that each hop in that live chain corresponds to an authorized entry in ads.txt and a disclosed identity in sellers.json. The three work as a system: ads.txt and app-ads.txt authorize sellers, sellers.json identifies them, and SupplyChain traces the real path of a given impression. Confusing them is common but avoidable, so remember that the publisher hosts ads.txt, the intermediary hosts sellers.json, and the bid stream carries SupplyChain. Each closes a different gap the others cannot, which is why the industry uses them in combination rather than choosing one.

For a publisher or intermediary, using sellers.json well means publishing an accurate, complete, and current file, listing every authorized seller with correct identifiers and honestly marking which entries are direct publishers and which are resellers, so buyers can trust what they find. Gaps and errors undermine the whole point, because a missing or wrong entry either blocks legitimate buying or hides a party that should be disclosed. For a buyer, using sellers.json well means actually checking it: cross-referencing the sellers in a bid against the file, tracing the SupplyChain object, and preferring inventory whose full path is disclosed and authorized. The standard only delivers transparency if both sides participate, publishers and exchanges by disclosing, buyers by verifying.

The failures are mostly failures of diligence. Publishing an incomplete or outdated sellers.json leaves authorized sellers undisclosed and defeats the transparency the file exists to provide. Confusing sellers.json with ads.txt, expecting the publisher to host the seller-identity file or the exchange to host the publisher's authorization file, leads teams to look in the wrong place. Treating the file as a fraud cure-all is another trap, because it makes the supply path legible but does not police it on its own. And ignoring the files entirely, on either side, throws away the cross-checks that catch misrepresented inventory. The discipline is to publish these files accurately, verify them as a buyer, and use sellers.json, ads.txt, and SupplyChain together as the transparency system they were designed to be.

Sellers.json was introduced by the IAB Tech Lab alongside ads.txt and the SupplyChain object to bring identity and transparency to the programmatic advertising supply chain.

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