MoPub launches support for app-ads.txt

May 08, 2019

Tags: 2019, Industry Perspectives, Publishers, DSPs, Marketers

Samantha Solmonson
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In a recent blog post, we discussed the importance of leveraging the IAB’s app-ads.txt spec in order to combat unauthorized reselling and app spoofing. As we have seen with the widespread adoption of its desktop counterpart, MoPub believes app-ads.txt will help create a trusted environment for in-app ad buying and selling. MoPub is happy to announce that we are now supporting the IAB’s most recent version of the app-ads.txt specification.

What is app-ads.txt?

In 2018, the IAB launched ads.txt, which is a file that web publishers use to designate authorized digital sellers of their ad inventory. App-ads.txt is the mobile in-app equivalent of this spec. App developers may now place the app-ads.txt file on their developer websites in order for DSPs to crawl and validate that they are receiving inventory through an authorized source.

How can publishers adopt app-ads.txt?

  1. Provide a developer website in their app store listings.

    • The publisher must ensure that the proper developer website URL is accessible in the developer website section of the app store.

  2. Publish an app-ads.txt file.

    • Include a list of authorized digital sellers along with the following information:

      • Ad source domain - For MoPub, this will be

      • Publisher ID - This is MoPub’s unique identifier for each publisher and can be retrieved under Account Settings in the MoPub UI.

      • Type of relationship - All of MoPub’s publisher relationships are direct, and therefore, the value for MoPub will always be designated as “direct.”

      • Ad source ID - This is the ad source’s TAG ID. For MoPub, this will be 74b46c0ea83967ca.

    • An example of the MoPub entry in a publisher’s app-ads.txt file can be found below (all four parameters are separated by a comma on a separate line for each authorized partner):, [pub id], DIRECT, 74b46c0ea83967ca

  • Publish the app-ads.txt file in the root of the app developer’s developer website (for example:

How can DSPs access app-ads.txt?

  1. Identify app store listing URLs.

    • MoPub passes the app store listing URL in the storeurl attribute of the app object in the bid request.

  2. Crawl app listing page in the app store.

    • The DSP will have to crawl the app listing page in the app store to identify the app developer’s developer webpage.

  3. Translate the developer URL into an app-ads.txt path.

    • Extract the host name portion of the URL.

    • Remove all but the first (and, if present, second) name from the host name which precedes the standard public suffix.

    • Remove any “www.” or “m.” prefix remaining in the host name.

    • Crawlers should attempt to fetch the HTTPS version of the URL first, falling back to the HTTP version if SSL is unavailable.

  4. Crawl and interpret the app-ads.txt file.

While this spec is optional, we encourage all publishers and DSPs to adopt app-ads.txt as a best practice to help further our industry’s overall transparency and trust.  For more information, please visit MoPub’s developer documentation for DSPs and for publishers or view the IAB Tech Lab’s specification in its entirety on its website. 

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