sellers.json Lookup

Runs in your browser · nothing sent, stored, or logged

The other half of the ads.txt check

ads.txt answers one question: which ad systems has this publisher authorised to sell its inventory, and under which account IDs. sellers.json answers the reciprocal one: for a given account ID, who is that ad system actually selling on behalf of. Walking both directions is what turns a bid request into a verified chain — you take the seller_id from the bid, look it up in the exchange's sellers.json, confirm the declared domain, then check that domain's ads.txt authorises the exchange under that same ID. A break anywhere in that loop is the signal that something is being misrepresented.

What a confidential seller really tells you

The spec allows a seller to withhold its name and domain, and there are legitimate reasons — commercial sensitivity about a media owner's monetisation partners, mainly. But a high proportion of confidential entries makes a supply path unverifiable by design, which is why many buyers now exclude them or apply a discount. It is worth checking the ratio rather than any single entry: an exchange where a handful of sellers are confidential looks quite different from one where a third of them are, and this tool reports the count so you can judge that at a glance.

These files are bigger and messier than people expect

A mid-sized exchange publishes several thousand sellers; the largest publish millions of lines and files over a hundred megabytes. They are also not uniformly valid. Spot-checking major platforms in July 2026 turned up entries with a seller_type outside the three the spec permits, and non-confidential sellers carrying no name at all — in a file from a top-tier SSP. None of that breaks a bid, which is exactly why it survives: nothing in the delivery path validates these files, so errors accumulate quietly until a buyer's supply-path rules start silently excluding inventory.

Frequently asked questions

What is the difference between PUBLISHER, INTERMEDIARY and BOTH?

PUBLISHER means the seller owns the inventory being sold. INTERMEDIARY means they are reselling someone else's. BOTH means they do each in different circumstances, which is common for large media groups. The type matters to a buyer because it says whether the chain ends here or continues.

Why do some sellers have no name or domain?

Because they are marked confidential, which the spec permits. A confidential seller must omit both name and domain — declaring is_confidential and then disclosing them anyway is a spec violation, and this tool flags it. Buyers with strict supply-path rules often exclude confidential sellers entirely.

How do I use this alongside ads.txt?

They are two halves of one check. A publisher's ads.txt names an ad system and an account ID; that account ID is the seller_id you look up here. If the seller_id is missing from the exchange's sellers.json, or its declared domain does not match the publisher, the chain does not verify.

Where is Google's sellers.json, and why can't I look it up here?

Not at google.com/sellers.json, which returns a 404 — it is published at realtimebidding.google.com/sellers.json, which redirects to Google Cloud Storage. It was 108 MB when last checked in July 2026, far past what can be parsed inside a serverless function, so this tool reports the size rather than hanging. For files that large, download directly and search locally with a streaming JSON tool.

Which domain do I enter for an exchange?

The domain that appears in the ads.txt line, which is usually the bare corporate domain — openx.com, pubmatic.com, indexexchange.com. A few large platforms publish on a subdomain instead, so if the bare domain 404s, check the ad system's documentation for the canonical location.

Is a seller_id stable over time?

It is meant to be, and buyers build supply-path rules on that assumption. In practice IDs do get retired and reissued during platform migrations, which is one reason to check a specific ID rather than trusting a spreadsheet that was accurate last quarter.