What is ads.txt & app-ads.txt?

Also known as: Authorized Digital Sellers

Quick definition

ads.txt (for websites) and app-ads.txt (for apps and CTV) are public text files hosted by a publisher that list every ad system and account ID authorized to sell its inventory, letting buyers reject unauthorized resellers and domain spoofing.

How it works

Publisher hosts /ads.txt on its domain (apps: on the developer site listed in the store)
Each line: ad system domain, seller account ID, DIRECT or RESELLER, optional cert authority ID
DSP crawls the file and matches it against the seller ID in each bid request
Unauthorized paths are filtered or deprioritized

Key points

Steward: IAB Tech Lab.
DIRECT vs RESELLER: DIRECT means the publisher controls the account; RESELLER means a third party is authorized to resell.
Pairs with: sellers.json and SupplyChain object to verify the entire path, not just the final seller.

Benefits

Cheap, public and easy to audit
Sharply reduced domain spoofing

Trade-offs

Files grow stale and bloated with unused reseller lines
Does not prove the traffic itself is human

FAQ

Where is app-ads.txt hosted?

On the developer website declared in the app store listing, at the root path /app-ads.txt.

Does AdTech Radar use app-ads.txt?

Yes. The AdTech Directory and Rankings are built from publicly fetched app-ads.txt supply chains.

Explore on AdTech Radar

Official sources

IAB Tech Lab – ads.txt

Last reviewed 2026-10-27. Explanations are written by AdTech Radar; consult the official specification for implementation.

Related terms

sellers.json & SupplyChain Object

sellers.json is a file published by an SSP or exchange that discloses the identity of each seller account it represents, while the SupplyChain object in the bid request records every hop the impression passed through; together with ads.txt they let buyers verify the full path from publisher to DSP.

Supply Path Optimization (SPO)

Supply path optimization is the practice of buyers choosing the fewest, cheapest and most transparent routes to the same publisher inventory, cutting redundant resellers so more of the media budget reaches the publisher.

Invalid Traffic (IVT)

Invalid traffic is any ad impression or click that does not come from a real, interested human, ranging from known data-center crawlers (GIVT) to sophisticated fraud such as bot farms, app spoofing and ad stacking (SIVT).