App-ads.txt is the public list of companies an app developer allows to sell ads in its apps. Paste one here and this checker counts the ad systems in it, splits the lines into DIRECT and RESELLER, and shows which ad systems appear most. It runs in your browser: the text you paste stays on your device.
What app-ads.txt is
The IAB Tech Lab, the ad industry's standards body, created ads.txt for websites and extended it to apps as app-ads.txt, "to fight inventory fraud for apps" (IAB Tech Lab). The app's store listing gives the developer's website, and the developer publishes the file there, listing "authorized sellers of their app's ad inventory" (IAB Tech Lab, app-ads.txt). Ad buyers check the list so they don't pay someone who isn't allowed to sell that app's ads.
Each record has up to four fields:
- Ad system domain: "the canonical domain name of the SSP, Exchange, Header Wrapper, etc system that bidders connect to".
- Account ID: the developer's or reseller's account on that ad system.
- DIRECT or RESELLER: DIRECT means the publisher "directly controls the account"; RESELLER means the publisher "has authorized another entity to control the account" and resell its ad space.
- Certification authority ID (optional): the ad system's ID at a certification authority such as the Trustworthy Accountability Group (TAG).
Lines like CONTACT= or OWNERDOMAIN= are variables, and a file with onlyplaceholder.example.com, placeholder, DIRECT, placeholdersays no one is authorized (IAB Tech Lab, ads.txt 1.1).
What the numbers do and don't tell you
- They show how the developer sells ads. A file with hundreds of ad systems, mostly RESELLER lines, means the developer's ad space is offered through a long chain of partners.
- They don't list the code inside the app. The file says who may sell the developer's ad space, not which ad SDKs are built in.
- One file covers every app from that website. If a developer publishes games and a VPN from the same site, the file is for all of them.
- No file doesn't prove there are no ads. It means the developer isn't taking part in this scheme: the IAB says publishing a website and its URL "is required for the app's ad inventory to participate" (IAB Tech Lab, app-ads.txt). To see what an app collects, read its privacy label on the App Store; how free VPNs make money walks through what to look for.
Why we checked free VPN apps
A VPN app sees all of your traffic, so how it pays for its servers matters. On November 10, 2026 we took the first 25 results each for "vpn" and "free vpn" in the US App Store search, kept free-to-download apps and removed duplicates and Mistero: 31 apps. 24 publish an app-ads.txt. The median file lists about 263 ad systems, the longest512, and 18 of the 24 list 100 or more. We don't name the apps: search results change, and a file is about the developer, not proof of what one app does. You can check any app yourself with this page.
For Mistero, the App Store listing has no developer website, there's no app-ads.txt on misterovpn.com, and the app has no advertising SDK: it's paid for by subscriptions. To check what any VPN changes on your connection, try the VPN test.
Questions
What is app-ads.txt?
A public text file on an app developer's website that lists the ad systems allowed to sell ads in the developer's apps. The IAB Tech Lab standard extends ads.txt for websites to apps: the App Store listing links to the developer's website, and the file sits at /app-ads.txt on that site.
What do DIRECT and RESELLER mean in app-ads.txt?
DIRECT means the developer controls that account on the ad system itself. RESELLER means the developer has authorized another company to control the account and resell the app's ad space through that ad system.
Does a long app-ads.txt mean an app is full of ad SDKs?
No. The file is a list of authorizations, not of code inside the app. It says who may sell the developer's ad space, not which SDKs are built in, and one file covers every app the developer publishes from that website. A long file does show that the developer offers its ad space through a lot of partners.
How do I find an app's app-ads.txt?
Open the app's App Store listing, tap Developer Website, and add /app-ads.txt to the site's address (without www.). Or type the website into this page and it builds the link. If there's no Developer Website or the file isn't there, the app isn't using app-ads.txt.