What does is_passthrough mean in a sellers.json entry?
Part of Supply path transparency
The short answer
is_passthrough is an optional sellers.json field that defaults to 0. Set to 1, it marks a seller whose inventory moves through a passthrough system, which the spec calls a facilitator of inventory from the upstream supplier to the consumer, and it means the buying system must hold its own account control relationship with that seller to transact.
Key takeaways
- The sellers.json spec defines a passthrough seller as "a facilitator of inventory from the upstream supplier to the consumer of the inventory."
- A value of 1 means the seller has an account control relationship with the downstream, consuming advertising system; 0 means it has none.
- IAB Tech Lab's FAQ says only the advertising system acting as a passthrough sets the flag, not the publishers or intermediaries that supply it.
- No public source measures how many sellers.json entries carry is_passthrough set to 1, so buyers count it in the files they use.
What does is_passthrough mean in sellers.json?
Definition
- is_passthrough
- An optional integer on a seller entry in a sellers.json file, default 0. A value of 1 says the named seller has an account control relationship with the downstream, consuming advertising system, so the inventory is being facilitated rather than resold.
The sellers.json specification (opens in a new tab), version 1.0 from July 2019, gives the definition in one sentence: "A passthrough seller is a facilitator of inventory from the upstream supplier to the consumer of the inventory." It adds that the upstream supplier and consumer must establish a business relationship with each other, such that the upstream supplier has control of its account within the consumer's platform.
| Value and position | What the spec says |
|---|---|
| 1, any position | This seller has an account control relationship with the downstream or consuming advertising system |
| 1, last link in the SupplyChain | The buying system has to have established an account control relationship with this seller to transact the seller's inventory |
| 1, not the last link | This seller should exist between two entities that have an account control relationship |
| 0, or the field absent | The downstream or consuming advertising system has no account control relationship with this seller |
The flag sits beside seller_type, not in place of it. The spec's own sample file shows an entry with seller_type PUBLISHER and is_passthrough 1, commented that the direct buyer or seller of this inventory must establish an account relationship with that publisher. The sellers.json guide covers seller_type and the other fields.
What is a passthrough seller, and who sets the flag?
IAB Tech Lab's FAQ for sellers.json and SupplyChain (opens in a new tab), dated July 2019 and updated September 2020, separates the role from reselling. It says a passthrough exchange is different from typical resell or ad network scenarios because it "acts only as a facilitator of inventory from the supplier of the inventory to the consumer of the inventory." The supplier keeps control of its own account on the buying side.
On who sets it, the FAQ is direct. The field is set when an advertising system requires the consuming system to hold a direct contractual relationship with the named entity. A system that receives the request and broadcasts it further does not set is_passthrough in its own file unless it, too, requires the receiver to hold a direct contract with the supply source.
How does a passthrough seller change the supply path?
The FAQ works through four exchange bidding cases. In each, ads.txt, sellers.json and the SupplyChain object have to agree on who pays whom. The table restates them with the FAQ's company names removed.
| Scenario | Who pays whom | ads.txt line | Where is_passthrough is 1 |
|---|---|---|---|
| Publisher through a passthrough provider | Bidding participant pays the provider; provider pays the publisher | DIRECT | The publisher's entry, seller_type PUBLISHER, in the provider's file |
| Reseller through a passthrough provider | Participant pays the provider; provider pays the reseller, which pays the publisher | RESELLER | The reseller's entry, seller_type INTERMEDIARY, in the provider's file |
| Exchange through a passthrough exchange | Buyer pays the passthrough exchange; it pays the first exchange | Same status as if the passthrough exchange were not involved | Entries for the first exchange in the passthrough exchange's file |
| Participant pays the publisher directly | Participant pays the publisher | DIRECT | No passthrough entry; the participant lists the publisher itself |
Each node in those chains carries hp set to 1. The SupplyChain specification (opens in a new tab) says hp marks a node involved in the flow of payment, and for version 1.0 should always be 1. Google's Authorized Buyers help on the SupplyChain object (opens in a new tab) says "Intermediaries that do not handle payment are not included in the SupplyChain Object." The passthrough provider in the FAQ handles payment, so it appears as a node.
How many sellers.json entries are marked passthrough?
No public primary source checked in October 2026 gives a count. The field is optional and defaults to 0, and the spec's examples show how it works, not how often it is used. A buyer who needs a number for its own paths can count it directly in the files of the exchanges it buys from, since sellers.json is public.
Count passthrough entries in one exchange's file
- Download the file. Fetch https://{exchange_domain}/sellers.json and save it with the date read.
- Count all entries. The spec says all sellers must be included even if confidential, so the sellers array is the full base.
- Count entries with is_passthrough set to 1. Treat a missing field as 0, its default.
- Split the count by seller_type. PUBLISHER and INTERMEDIARY entries with the flag are different cases in the FAQ.
- Match against the plan. Keep only entries whose seller IDs appear in the ads.txt files of the sites on the list, and date the result, since the spec's default expiry, without cache directives, is 7 days.
What should a buyer ask about passthrough sellers?
The spec's wording turns into practical questions, starting with the last link rule: if the passthrough entry is the final node, the buying system needs its own account control relationship with that seller. The Tech Lab's sellers.json page (opens in a new tab) tells buyers to review the SupplyChain object and verify identifiers within sellers.json files.
Questions to put to an exchange or DSP about a passthrough entry
- Which system's sellers.json carries the is_passthrough 1 flag, and on which seller ID?
- Does our buying platform hold the account control relationship the spec requires with that seller?
- Does the site's ads.txt list the passthrough system's account, and as DIRECT or RESELLER?
- Does the schain on live requests show the passthrough node with a sid matching that seller ID?
- Is the chain marked complete, and does its first node match the publisher in ads.txt?
- Who pays whom on this path, in the terms of the FAQ scenarios?
Authorization checks still apply. Google's Display & Video 360 help on authorized sellers (opens in a new tab) says the platform checks that every seller, including intermediaries, identified in the SupplyChain object is authorized. A passthrough label does not replace that check. The direct and reseller guide covers how the ads.txt side should line up.
What does a passthrough review look like on a real plan?
Fictional example
A flight school checks a passthrough path in Minnesota and Wisconsin
An unnamed flight school with training bases near Minneapolis, Duluth and Eau Claire runs display ads for its private pilot course on aviation, career and local news sites in English. Its agency reviews the supply paths for a curated deal before launch.
One aviation news site's ads.txt lists an account on a bidding provider as DIRECT. In that provider's sellers.json the entry is seller_type PUBLISHER with is_passthrough set to 1. The agency's exchange lists the provider as INTERMEDIARY, and live requests carry a complete two node schain.
The planner asks the exchange to confirm that the required account relationship with the publisher exists for this deal. It does, so the path stays, with a note recording the flag, the seller ID and the date each file was read.
How does PlacementGraph show who sells each site on a plan?
Frequently asked questions
Can a PUBLISHER entry in sellers.json be marked as passthrough?
Yes. The sellers.json spec's sample file includes an entry with seller_type PUBLISHER and is_passthrough set to 1, and the FAQ's first exchange bidding scenario does the same. The two fields answer different questions: seller_type says who owns the inventory and who is paid, and is_passthrough says whether the consuming system must hold an account relationship with that seller.
Does a passthrough system change what the publisher's ads.txt should say?
Not in the FAQ's examples. Where a provider passes a publisher's inventory through, the ads.txt line for the provider is DIRECT; where a reseller's inventory passes through, it is RESELLER. For an exchange passing another exchange's inventory, the FAQ says ads.txt keeps the same status as if the passthrough exchange were not involved.
Is a header bidding wrapper a passthrough seller?
Not by being a wrapper. The FAQ says technology vendors that are not in the direct payment chain between the buying system and the publisher should not be listed in the SupplyChain object and need no seller ID. A passthrough entry belongs to a system that facilitates and pays within the chain. The header bidding guide covers wrappers.
Does is_passthrough appear in the bid request?
No. It is a sellers.json field, read offline. The bid request carries the SupplyChain nodes, each with asi, sid and hp. A buyer joins them by looking up each node's sid in the sellers.json file on that node's asi domain, which is where the flag shows up.
Sources
- sellers.json specification, version 1.0 (opens in a new tab)IAB Tech Lab
- FAQ for sellers.json and SupplyChain Object (July 2019, updated September 2020) (opens in a new tab)IAB Tech Lab
- sellers.json (opens in a new tab)IAB Tech Lab
- SupplyChain object specification (opens in a new tab)IAB Tech Lab
- Bid transparency with the SupplyChain Object (opens in a new tab)Google Authorized Buyers Help
- Authorized Digital Sellers (opens in a new tab)Google Display & Video 360 Help
Researched and written by PlacementGraph Research. Read how we research, source and update these pages. Corrections: diana@placementgraph.com.