Reading ads.txt: what a publisher’s partner list tells you
ads.txt (Authorized Digital Sellers) is a plain text file that publishers place at the root of their domain. It lists every company allowed to sell the site’s advertising inventory. The IAB Tech Lab introduced it to make domain spoofing harder; as a side effect, it is one of the most useful public signals in publisher acquisition.
The anatomy of a line
google.com, pub-0000000000000000, DIRECT, f08c47fec0942fa0- Advertising system: the domain of the exchange or platform, here google.com.
- Account ID: the publisher’s or reseller’s account in that system.
- Relationship: DIRECT if the publisher controls the account, RESELLER if another company sells the inventory through its own account.
- Certification authority ID: optional, identifies the advertising system with the Trustworthy Accountability Group.
From account IDs to companies: sellers.json
An ads.txt line gives an account ID, not the name of whoever owns it. Advertising systems publish sellers.json files that map their account IDs to the companies behind them, and mark each seller as a publisher, an intermediary or both. Matching the RESELLER lines of a site against those files shows which partners already sell its inventory.
What the file tells you
- No file at all. The site probably does not sell programmatic inventory yet. Expect to explain the basics.
- Only google.com, DIRECT. The publisher runs Google’s products on its own. A partner can add demand and take over the management.
- Several RESELLER lines from one partner. Someone already manages the site’s monetization. Learn how satisfied the publisher is before you pitch.
- Dozens of resellers. Often a header bidding setup, sometimes a file copied from a template. Check that the lines match what the site actually loads.
Limits to keep in mind
ads.txt shows who is authorized, not who is active or how much they earn. Files go stale, because publishers rarely remove old lines, and a site’s own setup can block or redirect the file. Treat it as strong evidence, not proof, and confirm it in the conversation.
How PUBSONAR uses it
For every site, PUBSONAR reads ads.txt and matches the accounts against Google’s sellers.json and its list of Certified Publishing Partners. Discovery uses the result to keep or drop candidates, and the site panel lists the partners next to traffic and contacts, so the first letter can be specific.