Introducing the Ads.txt Validation Tool

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Today, in continuing support of the IAB’s ads.txt project, AppNexus is releasing an ads.txt validation tool to the public.  This free resource will help digital publishers ensure their ads.txt file is free of common errors we’ve observed many publishers make.

Based on our analysis of domains crawled on 10/4/2017, we believe a staggering 45% of all ads.txt files – representing thousands of domains – contain some kind of error. The use of non-canonical exchange URLs (e.g., listing instead of is far and away the most common cause.

Our goal is to help everyone implement a clean, consistent, and error-free file so that buy-side platforms can use ads.txt files to validate that every impression they bid on is coming from a legitimate seller.  At AppNexus, we already do that for buyers who use Console for Buyers, our demand-side platform, and we also deactivate supply on our exchange that isn’t declared by a publisher in their ads.txt files.


What common ads.txt file errors can this tool help me fix?


Currently, our validation tool checks for a variety of common issues we’ve seen from publishers:


  • File structure: Ads.txt files should have one partner per row, and at least three parameters per row.
  • Exchange URLs: Sometimes publishers aren’t sure exactly what domain they should use for an exchange. With AppNexus, for example, we’ve seen people use (which is the correct value) as well as ad server domains we use like This is more complex with organizations like AOL, which own a variety of ad technology companies, each with their own preferred domain. Using a non-canonical URL for a platform isn’t a guarantee a buyer won’t understand which platform you mean, but it is a risk, especially with less common exchanges.
  • Spelling: The tool checks for common misspellings we’ve seen; this is especially an issue on the direct / reseller parameter.


The tool allows you to enter an ads.txt URL or the entire contents of a file so you can validate the raw contents before posting it publicly. The tool will highlight any issues by row and describe them in detail in the sidebar.

Similarly, it’s also important to note what the tool does NOT do (at least, not yet):


  • Ensure the exchange IDs are valid: Be extra careful that you are typing your exchange IDs correctly and per your exchange’s documentation. For example, publishers working with AppNexus should list their four-digit AppNexus Member ID, which can be found in the lower left corner of the UI when logged in.  For AppNexus-specific documentation, click here.
  • Validate certificate authority IDs: This is the fourth, optional parameter publishers can list for a given exchange that declares their membership in related, anti-fraud programs like the Trustworthy Accountability Group, commonly referred to as TAG.


Over time, we’ll enhance this tool to be even smarter—let us know what you think in the comments. And feel free to promote this tool and the ads.txt program in general to help fight invalid traffic in the digital ad ecosystem!

Filed under AppNexus Updates, Technology.

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