App-Ads.txt Explained: Mobile App Advertising Transparency

What is app-ads.txt?

App-ads.txt (Authorized Digital Sellers for Apps) is an extension of the ads.txt standard designed to bring the same transparency and fraud prevention to mobile app and CTV app advertising. Released by the IAB Tech Lab, app-ads.txt allows app developers to publicly declare which advertising platforms are authorized to sell their in-app ad inventory.

The core problem app-ads.txt solves is the same as web ads.txt: preventing unauthorized entities from selling fake or misrepresented app inventory. In-app ad fraud has been a significant problem, with schemes like SDK spoofing (malware that generates fake ad impressions by mimicking legitimate app behavior) costing the industry hundreds of millions of dollars annually.

Why Apps Need a Different Approach

Web ads.txt is straightforward: a publisher places a file on their website, and buyers check it. But mobile and CTV apps do not have web domains in the same way. An app's identifier is its bundle ID (e.g., com.example.newsapp), not a URL. So how do you host a text file for an app?

The app-ads.txt solution uses the developer's website URL as listed in the app store (Google Play Store, Apple App Store, or CTV app stores). Here is how the linkage works:

1. Developer registers a website: When publishing an app, the developer lists their website URL in the app store (e.g., examplestudio.com).
2. Developer hosts app-ads.txt: The developer places an app-ads.txt file on that website (examplestudio.com/app-ads.txt).
3. Buyer receives bid request: The bid request for in-app inventory includes the app's bundle ID.
4. Buyer looks up developer website: Using the app store's data, the buyer finds the developer's website.
5. Buyer checks app-ads.txt: The buyer checks the app-ads.txt file on the developer's website to verify the seller is authorized.

app-ads.txt File Format

The app-ads.txt file format is identical to web ads.txt. Each line represents one authorized seller:

# app-ads.txt for ExampleStudio
google.com, pub-9876543210, DIRECT, f08c47fec0942fa0
pubmatic.com, 12345, DIRECT, 5d62403b186f2ace
inmobi.com, 98765abc, RESELLER, 83e75a7ae333ca9d
unity3d.com, 1234567, DIRECT
applovin.com, abcdef123, DIRECT

The four fields are the same as web ads.txt:

• Ad system domain: The SSP, ad network, or exchange domain
• Publisher/developer account ID: The app developer's account ID within that system
• Relationship type: DIRECT or RESELLER
• Certification authority ID: Optional TAG ID for verification

Implementing app-ads.txt: A Step-by-Step Guide

For Mobile App Developers

1. Ensure your app store listing has a website URL: In Google Play Console and App Store Connect, make sure your developer/publisher website is listed. This is the domain where you will host app-ads.txt.
2. Gather your advertising partner details: Collect the ad system domain, your account ID, and relationship type for every ad network, mediation platform, and SSP you work with.
3. Create the file: Create a plain text file named app-ads.txt with one entry per line.
4. Upload to your website root: Place the file at the root of the developer website listed in the app store (e.g., https://examplestudio.com/app-ads.txt).
5. Verify accessibility: Ensure the file returns a 200 HTTP status code and is publicly accessible.
6. Keep it updated: Add new partners and remove inactive ones as your monetization stack changes.

For CTV App Developers

The process for CTV apps is the same in principle, but the app stores differ:

• Roku: The developer website is listed in the Roku Channel Store developer portal.
• Amazon Fire TV: The developer website is in the Amazon Appstore listing.
• LG webOS: The developer website is in the LG Content Store listing.

CTV developers should pay special attention to app-ads.txt because CTV ad fraud is a growing concern and buyers are increasingly checking authorization before bidding.

How app-ads.txt Prevents In-App Ad Fraud

app-ads.txt targets several specific types of in-app ad fraud:

SDK Spoofing

Malicious apps run code that mimics ad SDK behavior, generating fake impressions and clicks that appear to come from legitimate apps. With app-ads.txt, buyers can verify whether the selling entity is actually authorized by the app developer, making SDK spoofing easier to detect.

App Spoofing / Bundle ID Fraud

Fraudulent sellers misrepresent low-quality apps as popular, high-value apps by falsifying the bundle ID in bid requests. app-ads.txt enables buyers to cross-check the seller against the legitimate app developer's authorized seller list.

Unauthorized Reselling

Entities that are not authorized by the app developer sell its inventory through intermediaries. app-ads.txt makes these unauthorized paths identifiable, allowing buyers to avoid them.

app-ads.txt Adoption in 2026

App-ads.txt adoption has grown steadily but still lags behind web ads.txt:

• Mobile apps: Adoption is strongest among top-grossing apps and apps that work with premium ad networks. Among the top 1,000 apps by ad revenue, adoption is high. The long tail of smaller apps has lower adoption.
• CTV apps: Adoption is still relatively early. Many CTV apps, especially smaller ones, have not yet implemented app-ads.txt. This is a known gap in CTV supply chain transparency.
• Platform variation: Adoption rates vary by app store and platform. Google Play apps tend to have higher adoption than CTV-only apps.

The trend is toward increasing adoption as DSPs enforce app-ads.txt in their bidding logic, similar to how web ads.txt enforcement drove publisher adoption.

Challenges with app-ads.txt

While app-ads.txt is a significant improvement, it faces some unique challenges compared to web ads.txt:

• Developer website dependency: Not all app developers maintain active websites, especially small indie developers. No website means no place to host app-ads.txt.
• App store data lag: Changes to developer website URLs in app stores may not propagate immediately, creating verification gaps.
• Multiple apps, one file: A developer with many apps hosts a single app-ads.txt file on their website. The file must cover all apps, which can become complex for large studios.
• CTV fragmentation: CTV platforms have different app store structures and developer portal systems, making consistent implementation challenging.

How Red Volcano Helps with app-ads.txt

Red Volcano crawls and analyzes app-ads.txt files across the mobile and CTV ecosystem:

• Mobile app coverage: app-ads.txt data for apps across the Google Play Store and Apple App Store, including authorized SSPs, account IDs, and relationship types.
• CTV app coverage: app-ads.txt analysis for CTV apps across Roku, Amazon Fire TV, and LG webOS.
• Adoption tracking: Monitor app-ads.txt adoption rates across platforms, app categories, and markets.
• SSP authorization analysis: For SSPs, see which apps authorize your platform and identify new onboarding opportunities.
• Change monitoring: Track when apps add or remove SSPs from their app-ads.txt files.
• Cross-platform intelligence: Understand the complete picture of an app developer's monetization stack across web, mobile, and CTV.