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.

s4c.cymru achieves the best ad optimization: its app-ads.txt has no errors and matches what its 3 ad networks expect (100% of 5 lines).

Checked 20 Oct 2026. 104 lines, 95 unique records, 2 duplicates, 0 invalid lines, 6 ad networks detected.

Google AdMob — account pub-4001305999037718: 1 line in the file
Magnite (Rubicon) — accounts 7908, 206615: 2 lines in the file
PubMatic — accounts 162069, 162087: 2 lines in the file
Mintegral — partner (reseller) lines only: 21 lines in the file, 400 expected lines missing
Chartboost — partner (reseller) lines only: 10 lines in the file, 400 expected lines missing
Yango Ads — partner (reseller) lines only: 24 lines in the file, 400 expected lines missing

Yes — https://s4c.cymru/app-ads.txt has 104 lines (checked 20 Oct 2026).

Its app-ads.txt lists Google AdMob, Magnite (Rubicon), PubMatic, Mintegral, Chartboost, Yango Ads.

s4c.cymru achieves the best ad optimization: its app-ads.txt has no errors and matches what its 3 ad networks expect (100% of 5 lines).