Definition
The SupplyChain Object — often shortened to schain — is an IAB Tech Lab standard that records the complete path an ad impression travels from the publisher to the buyer, carried inside the OpenRTB bid request itself. As an impression passes through each intermediary — SSPs, exchanges, resellers — each one adds a node to the SupplyChain Object, building an ordered list of every hop. By the time a buyer receives the bid request, the schain shows exactly which companies handled the impression, in order, all the way back to the origin.
If ads.txt answers “who’s authorized to sell this?” and sellers.json answers “who are these sellers?”, the SupplyChain Object answers “what route did this specific impression actually take?” It’s the piece that makes the transparency system dynamic — not just a static list to cross-check, but a live record of each impression’s real journey.
Disambiguation: The SupplyChain Object is the path layer of the three-part transparency system, and it’s distinct from the two static files. ads.txt is a file on the publisher’s site (authorization). sellers.json is a file on each intermediary’s site (identity). The SupplyChain Object isn’t a hosted file at all — it’s data passed within each bid request, unique to that impression, recording the actual route. It’s defined as part of the OpenRTB protocol. The three cross-reference: the nodes in a schain can be validated against the identities in sellers.json and the authorizations in ads.txt.
See also: ads.txt · sellers.json · Real-Time Bidding (RTB) · Supply Path Optimization (SPO)
Why it matters for marketing
The SupplyChain Object is what turns supply-chain transparency from a spot-check into a full audit trail. Before schain, a buyer receiving a bid request had limited visibility into how many intermediaries had touched the impression and taken a cut along the way. With it, the buyer sees the entire chain per impression and can ask the questions that matter: Is this path short and clean, or a long chain of resellers stacking fees? Does every node resolve to an identified, authorized seller? Is anything missing or suspicious?
That per-impression visibility is the backbone of supply path optimization. Buyers use SupplyChain Object data to compare the routes available for the same inventory and preferentially buy through the shortest, cleanest, cheapest ones — cutting redundant intermediaries and the fees they extract. It’s also a fraud and quality signal: an incomplete chain, or one with unverifiable nodes, is a reason to distrust the impression. For marketers trying to make sure their budget reaches real inventory efficiently, the schain is the most granular transparency tool the three-part system provides.
How it works
The SupplyChain Object is structured data attached to each bid request:
- A chain of nodes. The object contains an ordered array of nodes, one per intermediary that handled the impression. Each node identifies the seller with its advertising system identifier (its domain), a seller ID that matches the account in that seller’s sellers.json, and a flag for whether that node was paid for the transaction.
- Built up hop by hop. The publisher or first seller creates the initial object, and each subsequent intermediary appends its own node before passing the request on. The buyer receives the fully assembled chain.
- A “complete” flag. The object includes a flag indicating whether the chain represents the entire path back to the original publisher. A chain marked incomplete is a signal that visibility is missing — a caution for buyers.
- Cross-validation. Buyers validate each node against sellers.json (does this seller identity check out?) and ads.txt (is this seller authorized for this inventory?), reconstructing and verifying the full journey.
How to utilize the SupplyChain Object
- Map and compare supply paths. Use schain data to see every route available for a piece of inventory, then buy through the shortest, cleanest one. This is supply path optimization in practice.
- Flag incomplete or suspicious chains. Treat chains marked incomplete, or containing unverifiable nodes, as quality risks worth down-weighting or rejecting.
- Reduce fee stacking. Long chains mean more intermediaries taking margin. Preferring short chains directly improves how much of your spend reaches the publisher.
- Audit end to end. Combine schain with sellers.json and ads.txt to verify that every hop of an impression’s journey is identified and authorized.
Comparison: the SupplyChain Object in the transparency system
| Standard | Layer | Form | Scope |
|---|---|---|---|
| ads.txt | Authorization | Static file (publisher) | Who may sell |
| sellers.json | Identity | Static file (intermediary) | Who sellers are |
| SupplyChain Object | Path | Live data in each bid request | The actual route, per impression |
The SupplyChain Object is the dynamic layer — unlike the two static files, it’s specific to each impression and shows the real route taken. Validated against the other two, it makes the whole supply chain auditable per impression.
Best practices
- Require complete chains where you can. Prefer inventory with a complete SupplyChain Object over one marked incomplete. Missing visibility is a risk, not a neutral.
- Validate nodes against sellers.json. A schain is only as trustworthy as the identities in it. Cross-check each node so you’re not trusting an unverifiable seller.
- Favor shorter paths. Fewer nodes generally means fewer fees and less risk. Use schain length as one input into supply path decisions.
- Automate the checking. Per-impression validation across three standards is only feasible at scale with automation. Build or buy the capability rather than spot-checking.
- Intermediaries: pass it faithfully. For sell-side players, correctly building and forwarding the SupplyChain Object is now expected. Stripping or misrepresenting it undermines buyer trust.
Future trends
The SupplyChain Object has become a core input to automated supply path optimization, and as buyers get more sophisticated, real-time schain analysis increasingly drives which paths win the bid. The trajectory is toward fully automated, per-impression path scoring that weighs chain length, node verification, and fees together — making the schain less a thing humans inspect and more a signal machines act on continuously.
As with the rest of the transparency stack, the frontier is extending clean path recording into CTV, retail media, and other fast-growing programmatic environments where supply chains can be just as convoluted as on the open web. The persistent tension is completeness: an incomplete chain defeats the purpose, so industry pressure continues toward chains that represent the full path back to the publisher. The SupplyChain Object endures because it’s the only one of the three standards that captures what actually happened to a specific impression, rather than what was authorized or declared in advance.
FAQs
What is the SupplyChain Object? An IAB Tech Lab standard, part of OpenRTB, that records the complete path an ad impression travels from publisher to buyer. Each intermediary adds a node, so the buyer sees every hop the impression took.
How is it different from ads.txt and sellers.json? ads.txt and sellers.json are static files declaring authorization and identity in advance. The SupplyChain Object is live data in each bid request showing the actual route that specific impression took.
What’s in a SupplyChain Object node? Each node identifies an intermediary by its advertising system domain, a seller ID matching that seller’s sellers.json, and a flag for whether the node was paid. Nodes are ordered to show the sequence of hops.
What does the “complete” flag mean? It indicates whether the chain represents the entire path back to the original publisher. A chain marked incomplete signals missing visibility, which buyers may treat as a quality risk.
Why do advertisers use the SupplyChain Object? To see, per impression, exactly which intermediaries handled it and in what order. That visibility drives supply path optimization — choosing shorter, cleaner, cheaper routes — and helps detect fraud and fee stacking.
How does it support supply path optimization? By revealing every route available for the same inventory, so buyers can preferentially purchase through the shortest, most transparent path and cut redundant intermediaries and their fees.
Is the SupplyChain Object a file like the others? No. Unlike ads.txt and sellers.json, it isn’t a hosted file. It’s structured data passed within each OpenRTB bid request, unique to that impression.
How is it validated? Buyers cross-reference each node against sellers.json (to confirm identity) and ads.txt (to confirm authorization), reconstructing and verifying the impression’s full journey.
Related Terms
- ads.txt
- sellers.json
- Real-Time Bidding (RTB)
- Supply Path Optimization (SPO)
- Supply-Side Platform (SSP)
- Ad Exchange
- Invalid Traffic (IVT)
- Demand Path Optimization (DPO)
- Programmatic Advertising
- Demand-Side Platform (DSP)
Sources
- IAB Tech Lab — OpenRTB SupplyChain Object: https://iabtechlab.com/sellers-json/
- IAB Tech Lab — OpenRTB specification: https://iabtechlab.com/standards/openrtb/
- AdExchanger — Supply chain transparency: https://www.adexchanger.com/