Ads.txt

A text file that publishers place on their web server, configured by site administrators, that acts as a whitelist of authorized selling partners. It specifies exactly which supply-side platforms (SSPs) and ad exchanges are permitted to sell that publisher's inventory programmatically.

By declaring approved partners in this file, publishers give buyers a verifiable signal of legitimacy — any SSP or exchange not listed is, by implication, unauthorized. This mechanism is a foundational tool in combating ad fraud, particularly the reselling of counterfeit or spoofed inventory by parties with no real relationship to the publisher. The ads.txt standard was developed by the IAB Tech Lab and is widely adopted across the programmatic ecosystem.