SupplyChain Object (schain)

The SupplyChain Object (schain) is a structured field within an OpenRTB bid request that records, in order, every intermediary an ad impression passed through on its way from the publisher to the buyer. Standardized by the IAB Tech Lab, it makes the path of a programmatic impression machine-readable and verifiable.

How it works#

The object contains a complete flag and an array of nodes. Each node represents one hop in the chain and carries the intermediary's advertising-system domain (asi), its seller account ID (sid), and other fields. The nodes are listed in the order the impression travelled, so a buyer can read the whole route from origin to the current request. The complete flag signals whether every hop is declared.

Why it matters#

schain answers a question the other transparency standards can't on their own: not just who is authorized, but who actually handled this specific impression and in what order. Buyers cross-check each node against the exchange's sellers.json and the publisher's ads.txt to confirm every hop is legitimate and to see how many middlemen take a cut. That visibility into the ad supply chain is the foundation of supply path optimization and a key defense against undeclared reselling and fraud.

Related terms: ads.txt, sellers.json, OpenRTB, and Ad Supply Chain.