Key Takeaways

• Sellers.json is a file hosted by SSPs and exchanges that lists all authorized sellers and resellers of ad inventory

• It works alongside ads.txt to create transparency in the programmatic supply chain

• Introduced by IAB Tech Lab in 2019 to combat ad fraud and improve trust

• Publishers benefit from cleaner supply paths and potentially higher CPMs

• Adoption is now virtually required for participation in the programmatic ecosystem

The Transparency Problem Sellers.json Solves

The programmatic advertising ecosystem can be a bit like ordering food through multiple delivery apps simultaneously - you're not always sure where your meal is coming from or how many hands it passed through. Before Sellers.json came along, advertisers often struggled to verify exactly who was selling the ad inventory they were buying.

This lack of transparency created serious problems. Bad actors could easily misrepresent inventory, leading to ad fraud, brand safety issues, and money basically disappearing into a black hole of middlemen.

What Sellers.json Actually Is (In Plain English)

At its core, Sellers.json is just a simple JSON file (hence the name) that intermediaries like SSPs and exchanges host on their servers. Think of it as a directory of everyone authorized to sell ad inventory through their platform.

The file contains crucial details about each seller:

• Seller ID: A unique identifier for the publisher or reseller

• Seller Type: Whether they're a direct publisher, an intermediary, or both

• Name and Domain: The actual identity behind the ID (unless confidential)

• Is Confidential: A flag indicating if the seller wishes to remain anonymous

Here's what an actual Sellers.json entry might look like:

{
  "seller_id": "pub-7654321",
  "seller_type": "PUBLISHER",
  "name": "Example Publisher Inc",
  "domain": "example-publisher.com",
  "is_confidential": 0
}

The beauty is in the simplicity. This standardized format makes it easy for buyers to programatically verify who they're purchasing from. It's basically a digital ID card for everyone selling ads.

How Sellers.json Works With Ads.txt

Sellers.json doesn't work alone. It's designed to complement ads.txt, which publishers host on their domains to list authorized sellers of their inventory.

Here's how they work together:

1. Publisher perspective: A publisher lists authorized partners in their ads.txt file

2. SSP perspective: The SSP lists all publishers and resellers in their Sellers.json

3. Advertiser perspective: Advertisers can cross-reference both to verify the legitimacy of the supply path

This dual verification system creates a much more transparent ecosystem. If someone claims to sell inventory from a premium site but isn't listed in that site's ads.txt or the SSP's Sellers.json, alarms should immediately go off.

Why Publishers Should Care About Sellers.json

You might think, "I'm just a publisher, why should I care about a file on some SSP's server?" There are actually several good reasons:

1. Better CPMs: As buyers gain confidence in the legitimacy of inventory, they're often willing to pay more for it

2. Reduced unauthorized reselling: It's harder for shady middlemen to misrepresent your inventory

3. Supply path efficiency: Advertisers can identify and prefur more direct paths to your inventory, potentially reducing fees

4. Mandatory for participation: Many DSPs now filter out inventory that lacks proper Sellers.json and ads.txt implementation

According to Primis, the biggest ad buyers have declared they're only buying from sources that fully implement Sellers.json, making it essentially mandatory for serious publishers.

Common Challenges With Sellers.json

While the concept is straightforward, implementation hasn't been without issues:

1. Confidentiality conflicts: Some publishers want anonymity, which creates transparency gaps

2. Keeping data updated: As business relationships change, Sellers.json files need constant updating

3. Incorrect implementations: Simple errors can lead to lost revenue opportunities

4. Complexity at scale: Large exchanges may have thousands of entries to maintain

Another challenge noted by the IAB Tech Lab is that smaller publishers sometimes don't understand how to verify their proper inclusion in their partners' Sellers.json files.

How To Check Your Sellers.json Status

If you're a publisher working with programmatic partners, you should regularly verify your representation in their Sellers.json files:

1. Navigate to https://[ssp-domain.com]/sellers.json

2. Search for your publisher ID or domain name

3. Verify the information is correct and your seller_type is properly designated

Common SSP Sellers.json locations include:

• Google: https://adservice.google.com/sellers.json

• Xandr: https://platform.xandr.com/sellers.json

• OpenX: https://openx.com/sellers.json

The Future of Supply Chain Transparency

Sellers.json is part of a broader move toward complete supply chain transparency. The IAB Tech Lab's Supply Chain Object builds upon Sellers.json and ads.txt to provide a complete history of each impression.

We're moving toward a future where every step from publisher to advertiser is fully documented and verifiable, drasticaly reducing fraud and improving efficiency.

Final Thoughts

Sellers.json has rapidly become an essential component of the digital advertising ecosystem. While it adds some administrative overhead, the benefits of increased transparency, reduced fraud, and improved trust far outweigh the costs.

For publishers looking to maximize their programmatic revenue, ensuring proper implementation across all your monetization partners is no longer optional - it's table stakes.

Have questions about Sellers.json or other programmatic transparency tools? Drop a comment below and we'll help clarify!

This article is part of our Monetization Minis series, designed to explain key adtech concepts in a straightforward, non-technical way.