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.

marktplaats.nl achieves the best ad optimization: its app-ads.txt has no errors and matches what its 7 ad networks expect (100% of 18 lines).

Checked 19 Oct 2026. 63 lines, 51 unique records, 1 duplicates, 0 invalid lines, 7 ad networks detected.

Google AdMob — accounts pub-4111860161827675, ca-pub-4111860161827675, ca-mb-app-pub-4111860161827675 and 3 more: 6 lines in the file
Magnite (Rubicon) — accounts 16128, 18716, 20916: 3 lines in the file
Xandr (Microsoft) — accounts 8511, 7790, 7456 and 1 more: 4 lines in the file
Index Exchange — accounts 186241, 187410, 208799 and 1 more: 4 lines in the file
OpenX — account 540447717: 1 line in the file
PubMatic — accounts 158035, 158056, 162349: 3 lines in the file
TripleLift — accounts 14026, 14026-EB: 2 lines in the file

Yes — https://marktplaats.nl/app-ads.txt has 63 lines (checked 19 Oct 2026).

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

marktplaats.nl achieves the best ad optimization: its app-ads.txt has no errors and matches what its 7 ad networks expect (100% of 18 lines).