The Definitive Guide to sellers.json

What is sellers.json?

Sellers.json is an IAB Tech Lab specification that allows supply-side platforms (SSPs), ad exchanges, and ad networks to publicly declare the entities authorized to sell inventory through their platform. Published as a JSON file at the SSP's root domain, sellers.json is the supply-side counterpart to ads.txt.

While ads.txt lets publishers say "these SSPs can sell my inventory," sellers.json lets SSPs say "these publishers and resellers are in my network." Together, they form a bidirectional trust framework that enables programmatic buyers to verify every link in the supply chain before spending advertiser dollars.

The sellers.json specification was finalized by the IAB Tech Lab in 2019, building on the foundation laid by ads.txt in 2017. Its adoption has been critical to the industry's push toward full supply chain transparency.

Why sellers.json Matters

The programmatic advertising ecosystem is complex. Between a brand's ad budget and the publisher's webpage, inventory can pass through multiple intermediaries: DSPs, SSPs, exchanges, ad networks, and resellers. Each hop in this chain is a potential point of fraud or value leakage.

Sellers.json addresses this by making SSP-seller relationships public and verifiable. Here is why that matters:

For Buyers (DSPs, Agencies, Brands)

• Supply path verification: Buyers can check whether the seller ID in a bid request matches a legitimate entity in the SSP's sellers.json.
• Supply path optimization (SPO): By analyzing sellers.json across SSPs, buyers can identify the shortest, most efficient paths to publisher inventory and eliminate redundant intermediaries.
• Fraud prevention: Mismatched or missing seller entries are red flags that help buyers avoid fraudulent inventory.

For SSPs and Ad Networks

• Trust signaling: Maintaining an accurate, comprehensive sellers.json demonstrates transparency to buyers and can improve win rates on bid requests.
• Compliance: Major DSPs increasingly require sellers.json compliance. SSPs without it risk losing access to premium demand.
• Competitive differentiation: A clean, well-maintained sellers.json with minimal confidential entries signals a high-quality, transparent supply network.

Technical Specification: Inside a sellers.json File

A sellers.json file is a JSON document hosted at the SSP's root domain (e.g., https://ssp.com/sellers.json). The file contains metadata about the SSP and an array of seller objects.

Top-Level Fields

{
  "contact_email": "programmatic@ssp.com",
  "contact_address": "123 Ad Street, New York, NY",
  "version": "1.0",
  "identifiers": [
    {
      "name": "TAG-ID",
      "value": "abcdef123456"
    }
  ],
  "sellers": [...]
}

Seller Object Fields

Each entry in the sellers array represents one authorized seller and includes the following fields:

• seller_id (required): The unique identifier for the seller within the SSP's system. This must match the account ID used in ads.txt and bid requests.
• seller_type (required): One of PUBLISHER, INTERMEDIARY, or BOTH. Indicates whether the seller owns inventory directly, resells others' inventory, or does both.
• name (conditional): The legal or business name of the seller entity. Required unless is_confidential is set.
• domain (conditional): The primary business domain of the seller. Required unless is_confidential is set.
• is_confidential (optional): When set to 1, the SSP is not disclosing the seller's identity. While allowed by the spec, excessive confidentiality reduces transparency.
• comment (optional): A free-text field for additional context about the seller.

Example Seller Entry

{
  "seller_id": "pub-12345",
  "seller_type": "PUBLISHER",
  "name": "Example News Corp",
  "domain": "examplenews.com",
  "is_confidential": 0
}

sellers.json and the SupplyChain Object

Sellers.json works alongside the OpenRTB SupplyChain Object (schain) to provide end-to-end supply chain transparency. While sellers.json is a static file that lists all of an SSP's authorized sellers, the schain object is dynamic, included in individual bid requests to describe the specific chain of intermediaries for that particular impression.

Together, they work like this:

1. A bid request arrives at a DSP with an schain object listing each hop in the supply chain.
2. The DSP validates each hop by checking the advertising system's sellers.json for the seller ID.
3. The DSP also checks the publisher's ads.txt to verify the first hop is authorized.
4. If everything checks out, the DSP can bid with confidence that the supply path is legitimate.

The Confidentiality Question

One of the most debated aspects of sellers.json is the is_confidential field. When an SSP marks a seller as confidential, they withhold the seller's name and domain from the public file. The reasons SSPs give for this include:

• Protecting competitive business relationships
• Contractual obligations with sellers who demand privacy
• Preventing competitors from poaching their supply

However, from a buyer's perspective, confidential entries are problematic. If a DSP cannot verify who the seller is, they cannot fully validate the supply path. As a result, many DSPs apply lower bid prices to inventory from confidential sellers, or skip it entirely. The trend in 2026 is toward less confidentiality as buyers increasingly reward transparency with higher CPMs.

Analyzing sellers.json at Scale

For ad tech professionals, analyzing sellers.json files across the ecosystem reveals valuable intelligence:

• SSP network size: The number of sellers in an SSP's sellers.json indicates its network breadth.
• Confidentiality ratio: The percentage of confidential entries signals the SSP's transparency posture.
• Publisher vs. intermediary mix: A high ratio of PUBLISHER entries suggests direct supply; heavy INTERMEDIARY presence suggests resold inventory.
• Cross-SSP overlap: Analyzing which sellers appear across multiple SSPs reveals multi-homed publishers and common reseller networks.

Doing this manually is impractical at scale. Red Volcano automates this analysis across every major SSP.

How Red Volcano Helps with sellers.json

Red Volcano maintains the industry's most comprehensive sellers.json dataset, crawling and parsing files from hundreds of SSPs, exchanges, and ad networks. The platform provides:

• Complete SSP profiles: For every SSP, see total sellers, confidentiality rates, publisher vs. intermediary breakdown, and historical trends.
• Seller ID lookup: Search any seller ID across all SSPs to see everywhere that entity appears in the ecosystem.
• Change tracking: Monitor when SSPs add or remove sellers, with weekly diff reports.
• Cross-reference with ads.txt: Automatically verify that sellers.json entries match corresponding ads.txt declarations for bidirectional validation.
• Competitive intelligence: Compare SSP networks side by side to understand market positioning and supply overlap.