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.

How app-ads.txt works

app-ads.txt connects three public places: your app’s store listing, your developer website and the bid request. A buyer checks that all three agree before spending money on your impression.

The idea in one sentence

Only the owner of an app controls the developer website shown in its store listing — so a list of authorized sellers published there can’t be faked by a third party.

Step by step

The developer puts the website address in the app’s Google Play and App Store listing.
At the root of that website the developer publishes app-ads.txt — one line for each ad network or SSP account allowed to sell the app’s ad space.
Ad networks and buyers read the file regularly (usually once a day) and cache it.
A bid request arrives: it names the app and the seller — the ad system and the account ID.
The buyer looks for a line with that ad system and account in the app’s file. A match → the seller is authorized; no match → the request is skipped or bid lower.

What a line contains

google.com, pub-0000000000000000, DIRECT, f08c47fec0942fa0

Ad system domain — the network or SSP (google.com, applovin.com, unity3d.com…).
Account ID — your publisher account in that system, or the reseller’s account.
Relationship — DIRECT (your own account) or RESELLER (a partner sells for you). See DIRECT vs RESELLER.
Certification authority ID — optional TAG-ID of the ad system. See certification authority ID.

Where it can break

The store listing shows a different domain than the one hosting the file.
The file returns an HTML page, a redirect or an error instead of plain text.
A network’s partner (RESELLER) lines are missing — those sellers can’t be verified.
Typos in the domain or ID — the line matches nothing.

Check your app-ads.txt free

FAQ

How often do buyers read app-ads.txt?

Most ad systems re-crawl it about once a day, so changes take effect within a day or two.

Does app-ads.txt work for CTV and OTT apps?

Yes. The same standard covers mobile, CTV and OTT apps — the file lives on the developer website of the app’s store listing.

Related guides

All app-ads.txt guides