SupplyChain Object (schain)

De facto industry standard for supply chain transparency in programmatic advertising, maintained by IAB Tech Lab and adopted broadly across the ecosystem

The Supply Chain Object (schain) is an open industry specification developed and maintained by the IAB Tech Lab, introduced in 2019 as part of broader efforts to combat fraud and increase transparency in programmatic advertising. It functions as an extension to the OpenRTB protocol, embedding a structured list of all entities — SSPs, exchanges, resellers, and other intermediaries — that have handled a bid request before it reaches a DSP or buyer. Each node in the chain includes identifiers such as the seller's domain, seller ID, and whether the seller has a direct relationship with the publisher. The schain specification works in close conjunction with ads.txt and sellers.json, forming a trio of IAB Tech Lab transparency initiatives. While ads.txt declares which companies are authorized to sell a publisher's inventory and sellers.json maps seller IDs to company identities, schain provides real-time, per-impression visibility into the reselling path. This allows DSPs and buyers to verify that every hop in the supply chain is authorized and to filter out unauthorized or suspicious inventory paths. As a royalty-free, open standard rather than a commercial product, schain has no company headquarters, employees, or revenue. Its significance in the AdTech ecosystem is substantial: it is widely adopted across major SSPs, DSPs, and ad servers, and is considered a foundational building block for supply path optimization (SPO) and programmatic supply chain integrity. Compliance is strongly encouraged by major buyers and platforms, making it a de facto requirement for legitimate programmatic inventory trading.