ads.txt / sellers.json

ads.txt is a flat text file served at the root of a publisher's domain that declares which SSPs are authorized to sell the publisher's inventory. Each line lists an SSP's domain, the publisher's account ID at that SSP, and the relationship type (DIRECT or RESELLER). A DSP that sees a bid request claiming inventory from publisher X via SSP Y checks the publisher's ads.txt to confirm Y is authorized; if not, the DSP doesn't bid.

ads.txt was introduced by the IAB Tech Lab in 2017 to fight domain spoofing — fraud where bad actors claim premium inventory they don't actually own. Adoption is now universal among any publisher that wants meaningful DSP demand; sites without ads.txt files are systematically de-prioritized.

sellers.json is the symmetric file on the SSP side, declaring the SSP's authorized sellers — useful for verifying the end-to-end supply path. Together, ads.txt and sellers.json let a DSP cryptographically attest that the supply path it's bidding on is what it claims to be.

The CTV variant is "app-ads.txt" served at the developer's domain, which describes which SSPs can sell ad inventory inside the developer's apps. DOOH inherits the same model: each screen network publishes an app-ads.txt declaring its authorized SSPs. Trillboards' app-ads.txt is served at trillboards.com/app-ads.txt and is checked by every connected DSP before bid.