Glossary
What is ads.txt?
Also called: Authorized Digital Sellers, ads.txt file
ads.txt is a public text file at the root of a website that lists every company allowed to sell its ad inventory, and whether each is DIRECT or RESELLER.
हिंदी में पढ़ेंads.txt, short for Authorized Digital Sellers, is an IAB Tech Lab standard; the current version is 1.1. The file lives at the root of your domain, for example news.example/ads.txt. Each line names an ad system’s domain, your account ID there and the relationship, DIRECT or RESELLER. A fourth field, the certification authority ID, is optional.
Buyers check it before they bid. If a bid request names a seller account that is not in your file, it looks unauthorised, and Google’s Display & Video 360 skips unauthorised sellers by default. In AdSense, if the file exists but your publisher ID is missing, Google will not buy ads on those requests, and your account shows an alert.
The common traps are simple: the file sits in a subfolder, the www and bare domain do not reach the same file, or robots.txt blocks it. Changes can take a few days to be picked up, so do not remove a correct file while you wait.
Example
Say a buyer sees 1,000 requests for news.example. 900 come through seller account 4521, listed as <code>ssp.example, 4521, DIRECT</code>. 100 come through account 9999, which is not in the file. A buyer that skips unauthorised sellers can bid only on the 900, or 90%.
Why it matters to publishers
A missing or broken line can stop buyers, including Google, from bidding on your inventory. Checking the file takes minutes.