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.

theguardian.com achieves the best ad optimization: its app-ads.txt has no errors and matches what its 8 ad networks expect (100% of 13 lines).

Checked 20 Oct 2026. 37 lines, 28 unique records, 1 duplicates, 0 invalid lines, 8 ad networks detected.

Amazon Publisher Services — account 76f5f9c9-7d79-4adc-9b0d-f248ebe3f5f7: 1 line in the file
Index Exchange — accounts 205118, 184842: 2 lines in the file
OpenX — accounts 559090935, 564251974: 2 lines in the file
PubMatic — accounts 161064, 157189: 2 lines in the file
TripleLift — accounts 2816, 2885-EB, 2885: 3 lines in the file
Xandr (Microsoft) — account 2888: 1 line in the file
Google AdMob — accounts pub-1452170585655900, pub-2012933198307164, pub-4979300716531995 and 3 more: 6 lines in the file
Magnite (Rubicon) — account 26644: 1 line in the file

Yes — https://theguardian.com/app-ads.txt has 37 lines (checked 20 Oct 2026).

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

theguardian.com achieves the best ad optimization: its app-ads.txt has no errors and matches what its 8 ad networks expect (100% of 13 lines).