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.

bbc.com achieves the best ad optimization: its app-ads.txt has no errors and matches what its 8 ad networks expect (100% of 19 lines).

Checked 19 Oct 2026. 79 lines, 54 unique records, 0 duplicates, 0 invalid lines, 8 ad networks detected.

Xandr (Microsoft) — account 12067: 1 line in the file
Amazon Publisher Services — accounts 5157, 1898770d-3169-4d27-b5b7-9538af253af1: 2 lines in the file
Google AdMob — account pub-2855034486820621: 1 line in the file
Index Exchange — accounts 184803, 199703, 213599: 3 lines in the file
OpenX — accounts 540222416, 557333401, 563701590: 3 lines in the file
PubMatic — accounts 157339, 161842, 166129: 3 lines in the file
Magnite (Rubicon) — accounts 17264, 12198: 2 lines in the file
TripleLift — accounts 918-EB, 918, 14807-EB and 1 more: 4 lines in the file

Yes — https://bbc.com/app-ads.txt has 79 lines (checked 19 Oct 2026).

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

bbc.com achieves the best ad optimization: its app-ads.txt has no errors and matches what its 8 ad networks expect (100% of 19 lines).