Definition
sellers.json is an IAB Tech Lab standard that lets advertising intermediaries — SSPs, ad exchanges, and networks — publicly declare the identities of every seller and intermediary they work with. Each SSP or exchange hosts a sellers.json file on its own domain, listing the seller accounts it transacts through: the seller’s ID, name, domain, and whether that seller is a publisher, an intermediary, or both. It’s the seller-side counterpart to ads.txt, and together they let a buyer verify not just that a seller is authorized but who that seller actually is.
Introduced in 2019, sellers.json answers a question ads.txt alone can’t: when a publisher’s ads.txt authorizes “SSP X, account 12345,” who is account 12345? sellers.json is where SSP X publicly identifies that account. Cross-reference the two and the anonymity that once hid intermediaries and fraud in the programmatic chain largely disappears.
Disambiguation: sellers.json is the identity layer in the three-part supply-chain transparency system. ads.txt (published by publishers) says who is authorized to sell. sellers.json (published by SSPs and exchanges) says who those authorized sellers are. SupplyChain Object (passed in the bid request) says what path the impression actually traveled. sellers.json is specifically about revealing seller and intermediary identities, closing the anonymity that ads.txt’s account IDs on their own would leave open.
See also: ads.txt · SupplyChain Object (schain) · Supply-Side Platform (SSP) · Supply Path Optimization (SPO)
Why it matters for marketing
sellers.json pulls back the curtain on the middlemen in the programmatic supply chain, which is exactly what advertisers need to spend efficiently and safely. For years, an impression could pass through a chain of intermediaries whose identities were opaque — and opacity is where hidden fees, arbitrage, and fraud thrive. By requiring SSPs and exchanges to publicly identify every seller, sellers.json lets buyers see who’s actually in the chain, which is foundational to supply path optimization: you can’t trim intermediaries you can’t see.
For marketers, the practical payoff is accountability. Combined with ads.txt and the SupplyChain Object, sellers.json lets a buyer trace an impression from the bid request back through each intermediary to the originating publisher, verifying at each step that the seller is authorized and identified. That end-to-end auditability is what makes it possible to detect invalid traffic, spot suspicious arbitrage, and choose cleaner, more direct paths. It’s less famous than ads.txt but does the essential work of turning anonymous account IDs into named, accountable companies.
How it works
sellers.json operates alongside ads.txt and the SupplyChain Object as a public, crawlable record:
- Each intermediary publishes the file. An SSP or exchange hosts
sellers.jsonat its domain, listing every seller account it works with — the seller ID (matching the account IDs that appear in publishers’ ads.txt files), the seller’s name and domain, and a seller type. - Seller types. Each entry is marked PUBLISHER (the seller owns the inventory), INTERMEDIARY (the seller resells others’ inventory), or BOTH. This reveals whether a given account is an original publisher or a reseller.
- Confidential entries. The standard allows some seller identities to be marked confidential, which is a point of ongoing debate — confidentiality preserves some business privacy but reduces the transparency the standard exists to provide.
- Cross-referencing. Buyers combine sellers.json with ads.txt and the SupplyChain Object: ads.txt authorizes an account, sellers.json identifies who that account is, and the SupplyChain Object shows the full route. Together they reconstruct and verify the impression’s origin.
How to utilize sellers.json
- Identify the intermediaries you’re buying through. Use sellers.json to see exactly which companies sit in your supply paths, then decide which to keep and which to bypass.
- Detect suspicious resale. Long chains of INTERMEDIARY entries, or accounts that don’t resolve to real publishers, can signal arbitrage or fraud worth investigating.
- Support supply path optimization. sellers.json is a core input for mapping and shortening supply paths — reducing hidden fees and reaching inventory more directly.
- Verify end to end. Cross-reference sellers.json with ads.txt and the SupplyChain Object to confirm every hop in an impression’s journey is authorized and identified.
Comparison: sellers.json in the transparency system
| Standard | Layer | Published by | Reveals |
|---|---|---|---|
| ads.txt | Authorization | Publishers | Who may sell this inventory |
| sellers.json | Identity | SSPs / exchanges | Who those sellers are |
| SupplyChain Object | Path | Each hop in the bid request | The route the impression traveled |
sellers.json is the identity bridge: ads.txt lists authorized account IDs, and sellers.json says who those account IDs belong to. Without it, ads.txt’s authorization would still leave intermediaries anonymous.
Best practices
- Cross-reference, don’t read it alone. sellers.json is most powerful combined with ads.txt and the SupplyChain Object. Any one of the three is a partial view.
- Scrutinize confidential entries. Sellers marked confidential reduce transparency. Weigh how much confidential inventory sits in a path and whether that’s acceptable for your buying.
- Watch for excessive intermediation. Chains dominated by INTERMEDIARY entries add fees and risk. Prefer paths that resolve quickly to PUBLISHER sellers.
- Intermediaries: keep it accurate and complete. For SSPs and exchanges, a thorough, current sellers.json is now expected by buyers. Gaps or stale entries undermine trust.
- Use it to inform, not just to audit. Beyond fraud detection, sellers.json shapes which supply paths you choose to buy through in the first place.
Future trends
sellers.json has become a standard expectation for legitimate SSPs and exchanges, and the industry conversation has shifted from “do you publish it?” to “how complete and honest is it?” The debate over confidential entries continues, balancing intermediaries’ business-privacy concerns against buyers’ demand for full transparency — and the pressure is generally toward more disclosure, not less, as buyers reward transparency with spend.
Like the other transparency standards, sellers.json is being pulled into an integrated verification stack rather than used in isolation. As supply path optimization matures and buyers get more sophisticated about inventory quality, automated systems increasingly cross-reference all three standards in real time to score and select supply paths. The migration of programmatic into CTV and retail media brings the same need for seller identity into new environments, extending sellers.json’s relevance well beyond the open web where it started.
FAQs
What is sellers.json? An IAB Tech Lab standard where SSPs, exchanges, and networks publicly publish the identities of every seller and intermediary they work with — the seller-side counterpart to ads.txt.
How is sellers.json different from ads.txt? ads.txt, published by publishers, lists the account IDs authorized to sell their inventory. sellers.json, published by SSPs and exchanges, reveals who those account IDs actually belong to. Together they provide authorization and identity.
What information is in a sellers.json file? For each seller: a seller ID (matching ads.txt account IDs), the seller’s name and domain, and a type — PUBLISHER, INTERMEDIARY, or BOTH — indicating whether they own the inventory or resell it.
What are confidential entries in sellers.json? Entries where a seller’s identity is withheld for business-privacy reasons. They’re allowed by the standard but debated, since they reduce the transparency sellers.json exists to provide.
Why do advertisers care about sellers.json? Because it reveals the intermediaries in their supply paths. Seeing who’s in the chain lets buyers detect suspicious resale, reduce hidden fees, and choose cleaner, more direct paths — the basis of supply path optimization.
How does sellers.json help fight fraud? By removing anonymity. When every seller must be publicly identified and cross-referenced against ads.txt and the SupplyChain Object, it’s much harder for fraudulent or unauthorized intermediaries to hide in the chain.
Who publishes sellers.json? Advertising intermediaries — SSPs, ad exchanges, and networks — each host their own file. Publishers publish ads.txt; intermediaries publish sellers.json.
How does it relate to the SupplyChain Object? sellers.json identifies who sellers are; the SupplyChain Object shows the actual path an impression took through those sellers. Cross-referenced, they let buyers reconstruct and verify the full journey.
Related Terms
- ads.txt
- SupplyChain Object (schain)
- Supply-Side Platform (SSP)
- Supply Path Optimization (SPO)
- Ad Exchange
- Invalid Traffic (IVT)
- Programmatic Advertising
- Demand-Side Platform (DSP)
- Curation
- Real-Time Bidding (RTB)
Sources
- IAB Tech Lab — sellers.json specification: https://iabtechlab.com/sellers-json/
- IAB Tech Lab — Supply Chain Transparency: https://iabtechlab.com/ads-txt/
- AdExchanger — sellers.json and supply chain transparency: https://www.adexchanger.com/