An IAB Tech Lab standard that lets app publishers declare which ad networks are authorized to sell their inventory.

Where do I put the app-ads.txt file?

At the root of the developer website listed in your App Store / Google Play page, e.g. https://studio.com/app-ads.txt.

What is a Certification Authority ID?

An optional TAG-ID of the ad system, the 4th field of an app-ads.txt record.

nationalgeographic.com achieves the best ad optimization: its app-ads.txt has no errors and matches what its 5 ad networks expect (100% of 5 lines).

Checked 19 Oct 2026. 107 lines, 101 unique records, 3 duplicates, 0 invalid lines, 5 ad networks detected.

Google AdMob — accounts pub-5653662817748324, pub-7154879651992621, pub-7442541831975590 and 6 more: 9 lines in the file
Index Exchange — account 191125: 1 line in the file
Magnite (Rubicon) — account 12004: 1 line in the file
Amazon Publisher Services — account 66ccb8d5-78f3-42f1-b80c-4ed5f9d8d2a6: 1 line in the file
Xandr (Microsoft) — account 9446: 1 line in the file

Yes — https://nationalgeographic.com/app-ads.txt has 107 lines (checked 19 Oct 2026).

Its app-ads.txt lists Google AdMob, Index Exchange, Magnite (Rubicon), Amazon Publisher Services, Xandr (Microsoft).

nationalgeographic.com achieves the best ad optimization: its app-ads.txt has no errors and matches what its 5 ad networks expect (100% of 5 lines).