What is ads.txt?
ads.txt is a plain text file a publisher hosts at the root of its website, for example example.com/ads.txt, listing every advertising system authorized to sell its inventory and the publisher's account ID in each. Published by IAB Tech Lab, it lets buyers reject inventory offered through an exchange or account the publisher never named. App inventory uses the parallel app-ads.txt file.
Also called: ads txt, Authorized Digital Sellers, adstxt.
How it works
Each record line holds the advertising system's domain, the publisher's account ID on that system, and the relationship, DIRECT or RESELLER, optionally followed by a certification authority ID. A line such as ssp.example, 4921, DIRECT says the publisher itself controls account 4921 on ssp.example. The file can also carry variables, for example a contact address or the domain of an inventory partner allowed to sell part of the inventory.
A buyer checks a bid request against ads.txt by taking the domain in Site.domain, fetching that domain's ads.txt, and looking for a line that matches the seller. When the request carries a supply chain, the match is made on the first node that is paid, using SupplyChainNode.asi as the system domain and SupplyChainNode.sid as the account ID. That account ID is normally the same value the exchange sends in Publisher.id.
Failures are usually stale or partial files. A missing line or a mistyped account ID breaks the match, and many bidders then stop bidding or return no-bid reason 12 (Ads.txt Authorization Violation), or 11 when no file could be fetched. ads.txt only says who may sell. It says nothing about the path a specific request took, which is what sellers.json and the supply chain object add.
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Related terms
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