What is sellers.json? A Complete Explanation

What is sellers.json?

Sellers.json is a transparency standard created by the IAB Tech Lab that allows supply-side platforms (SSPs), ad exchanges, and ad networks to publicly declare all the entities that sell advertising inventory through their system. It is a machine-readable JSON file hosted at the SSP's root domain.

If ads.txt is a publisher saying "I authorize these platforms to sell my ads," then sellers.json is the platform saying "these are all the publishers and resellers in my network." Together, they create a two-way trust system that helps buyers verify every link in the advertising supply chain.

Why sellers.json Exists

The programmatic advertising ecosystem is complex. Between an advertiser's budget and a publisher's webpage, inventory can pass through multiple intermediaries. Each intermediary is a potential point of fraud, value leakage, or opacity.

Before sellers.json, if a buyer received a bid request from an SSP with a seller ID of "12345," there was no standardized way to verify who seller 12345 actually was. Was it a legitimate publisher? A reseller? An unknown entity? Sellers.json answers this question by making the SSP's seller directory public.

The Trust Triangle

Sellers.json is one leg of what the industry calls the transparency "trust triangle":

1. ads.txt (publisher-side): Publisher declares "SSP X can sell my inventory"
2. sellers.json (SSP-side): SSP X declares "Seller 12345 is ExampleNews.com, a direct publisher"
3. SupplyChain Object (bid-level): The bid request includes the full chain of intermediaries for this specific impression

When all three align, the buyer has high confidence in the legitimacy of the supply path.

How to Read a sellers.json File

A sellers.json file is a JSON document. Here is a simplified example:

{
  "contact_email": "support@example-ssp.com",
  "version": "1.0",
  "sellers": [
    {
      "seller_id": "pub-001",
      "seller_type": "PUBLISHER",
      "name": "Example News",
      "domain": "examplenews.com",
      "is_confidential": 0
    },
    {
      "seller_id": "reseller-002",
      "seller_type": "INTERMEDIARY",
      "name": "Ad Network Co",
      "domain": "adnetwork.com",
      "is_confidential": 0
    },
    {
      "seller_id": "anon-003",
      "is_confidential": 1
    }
  ]
}

Key Fields Explained

• seller_id: The unique identifier for this seller within the SSP's system. This is the same ID that appears in ads.txt and bid requests.
• seller_type: Indicates the seller's role:
  • PUBLISHER — a direct content publisher that owns inventory
  • INTERMEDIARY — a company that resells others' inventory
  • BOTH — the entity both publishes content and resells others' inventory
• name: The seller's business name (hidden if confidential)
• domain: The seller's primary domain (hidden if confidential)
• is_confidential: When set to 1, the SSP withholds the seller's identity

Understanding Confidential Entries

One of the most discussed aspects of sellers.json is the confidentiality flag. When an SSP marks a seller as confidential, they reveal only the seller_id and seller_type but hide the name and domain.

SSPs use confidentiality for various reasons:

• Protecting competitive business relationships from rival SSPs
• Contractual obligations with sellers who demand privacy
• Early-stage partnerships where the publisher is not yet ready for public listing

However, from the buyer's perspective, confidential entries are a transparency gap. If you cannot verify who the seller is, you cannot fully validate the supply path. As a result:

• Many DSPs bid lower on inventory from confidential sellers
• Some DSPs skip confidential sellers entirely
• Industry pressure is pushing SSPs toward lower confidentiality rates

Red Volcano tracks confidentiality rates across all SSPs, making this an easy metric to compare when evaluating supply partners.

How sellers.json Works with ads.txt

Sellers.json and ads.txt are designed to work together. Here is a practical example of cross-verification:

1. A buyer receives a bid request from PubMatic with seller_id "pub-12345" claiming to represent examplenews.com.
2. The buyer checks PubMatic's sellers.json: Does seller_id "pub-12345" exist? Is it listed as examplenews.com? Is it a PUBLISHER type?
3. The buyer checks examplenews.com/ads.txt: Is pubmatic.com listed with account ID "pub-12345" and type DIRECT?
4. If both check out, the buyer has high confidence the supply path is legitimate.

This bidirectional verification is a powerful fraud prevention mechanism. Red Volcano automates this cross-referencing at scale.

What sellers.json Reveals About an SSP

Analyzing an SSP's sellers.json file reveals a great deal about its business:

• Network size: The total number of sellers indicates the SSP's scale. Major SSPs may have tens of thousands of sellers.
• Publisher vs. intermediary ratio: A high proportion of PUBLISHER entries suggests direct supply; heavy INTERMEDIARY presence suggests reliance on resold inventory.
• Confidentiality rate: The percentage of confidential entries signals the SSP's transparency posture. Lower is generally better from a buyer's perspective.
• Growth trends: Tracking sellers.json changes over time reveals whether the SSP's network is growing, shrinking, or churning.
• Seller quality: Analyzing the domains and names of sellers can indicate the quality of the SSP's supply.

How Red Volcano Helps with sellers.json Data

Red Volcano provides the most comprehensive sellers.json dataset in the industry:

• Complete coverage: We crawl sellers.json from every major SSP, exchange, and ad network, parsing and structuring the data for easy analysis.
• SSP profiles: Each SSP in our database has a detailed profile including seller counts, confidentiality rates, publisher vs. intermediary breakdown, and historical trends.
• Cross-reference engine: Search any seller ID, domain, or company name across all SSPs to see everywhere they appear in the ecosystem.
• Change monitoring: Weekly diffs show when SSPs add, remove, or modify seller entries.
• Bidirectional validation: Automatic cross-referencing of sellers.json with ads.txt data to flag mismatches and verify supply chain integrity.