Sellers.json File Explained

Sellers.json Explained: Why It Matters in Digital Advertising

Let’s talk about transparency in digital advertising. If you’ve ever dabbled in programmatic ads, you know that figuring out who’s actually selling ad inventory can feel like detective work. That’s where Sellers.json comes in—it’s like an industry-wide phonebook for ad sellers, helping advertisers verify who they’re buying from. It was developed by the Interactive Advertising Bureau (IAB) Tech Lab to combat fraud, build trust, and clean up the digital ad space.

What Exactly is Sellers.json?

Think of Sellers.json as a publicly accessible file hosted by ad platforms like supply-side platforms (SSPs) and ad exchanges. It lists out all the entities involved in selling digital ad inventory, making it easier for advertisers and demand-side platforms (DSPs) to confirm whether they’re dealing with legitimate sellers.

Here’s why it matters: without a tool like this, shady resellers can misrepresent inventory, making it harder for advertisers to trust where their money is going. Sellers.json helps solve this problem by distinguishing between direct publishers (who own the inventory) and intermediaries (who resell it).

Another cool feature? Offline verification—instead of bloating every bid request with seller details, ad platforms can refer to the Sellers.json file when needed, keeping transactions lightweight while still being transparent.

Why Was Sellers.json Created?

Before Sellers.json, advertisers had a tough time confirming who they were actually buying from. There was Ads.txt, which helped publishers specify which platforms could sell their inventory, but it had a big blind spot—it didn’t reveal who those sellers actually were. That lack of transparency opened the door for domain spoofing (where scammers pretend to be premium publishers).

To fix this, IAB Tech Lab launched Sellers.json in 2019, ensuring that advertisers could see exactly who was in the supply chain. Now, with both Ads.txt and Sellers.json, we’ve got a clearer, more fraud-resistant ecosystem.

Sellers.json vs. Ads.txt: What’s the Difference?

These two standards work together, but they serve different purposes:

Ads.txt (Authorized Digital Sellers) is hosted by individual publishers to declare which ad platforms are allowed to sell their inventory. It tells advertisers where they can buy but doesn’t disclose who the seller actually is.
Sellers.json, on the other hand, is hosted by SSPs and ad exchanges and lists all the real entities behind those sales. This means advertisers can verify if they’re buying from a direct publisher or a middleman.

In short: Ads.txt controls authorization, while Sellers.json provides identity.

What About the OpenRTB Supply Chain Object?

Sellers.json isn’t the only tool designed for transparency. Enter the OpenRTB Supply Chain Object, a real-time transparency tool that lives inside bid requests.

While Sellers.json is a static file listing all a platform’s sellers, the Supply Chain Object is dynamic—it tracks each bid request as it moves through multiple intermediaries. This way, advertisers can see the exact path an impression took before reaching them.

Together, these tools help advertisers make smarter, more informed buying decisions.

How to Implement Sellers.json

Setting up Sellers.json isn’t complicated, but there are some rules to follow. Here’s what you need to do:

1. Host the File Publicly

SSPs and ad exchanges must host their Sellers.json file at the root domain so it’s easy to find. The URL should look like this:

https://yourdomain.com/sellers.json

It needs to be accessible via HTTP/HTTPS so advertisers and crawlers can verify seller details.

2. Follow the Correct Format

Sellers.json is written in JSON format and includes key details about each seller. Here’s what a basic file looks like:

{
  "sellers": [
    {
      "seller_id": "123456",
      "name": "Example Publisher",
      "domain": "examplepublisher.com",
      "seller_type": "PUBLISHER"
    },
    {
      "seller_id": "789101",
      "name": "Ad Network Inc.",
      "domain": "adnetwork.com",
      "seller_type": "INTERMEDIARY"
    }
  ]
}

3. Keep It Updated

Sellers.json isn’t a “set it and forget it” file. SSPs and ad exchanges must update it regularly to reflect any changes in their seller relationships.

4. Handle Confidential Sellers

Some sellers may not want their identity made public. In this case, they can set the is_confidential flag to 1. However, transparency is always encouraged—advertisers prefer to work with sellers they can fully verify.

FAQ

Do publishers need to host Sellers.json files?

Nope! Publishers don’t need to host their own Sellers.json file. Their SSP or ad exchange will handle it for them. However, publishers should check that their information is correctly listed.

How often should Sellers.json files be updated?

Regularly! SSPs and ad exchanges should update their files whenever partnerships change to maintain accuracy.

Can sellers be confidential in Sellers.json?

Yes, but transparency is preferred. Sellers can set their is_confidential flag to 1, but advertisers may hesitate to buy from unidentified sellers.

What’s the difference between Sellers.json and the Supply Chain Object?

Sellers.json is a public file that lists all the sellers working with an SSP or exchange.
The Supply Chain Object is included in bid requests and shows the real-time path of a specific impression.

Using both together ensures transparency at both the macro and micro levels.

Final Thoughts

Sellers.json is a big step toward cleaning up programmatic advertising. By making seller identities public, it helps advertisers make more informed decisions, reduces fraud, and strengthens trust across the ecosystem.

If you’re in the ad tech space, implementing and maintaining Sellers.json isn’t just best practice—it’s a necessity for staying credible in a rapidly evolving industry.