Ads.txt Specification

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Ads.txt has fast gained attention as an impactful tool in fighting fraud. Publishers can post a list of Authorized Digital Sellers to declare allowed sellers and resellers of the publisher’s inventory. Buyers can use ads.txt files to shift media spend to authorized supply paths. The goal is that publishers will receive revenue for ads purchased from their inventory, and buyers will not waste spend on fraudulent inventory. IAB Tech Lab’s OpenRTB Working Group developed the ads.txt specification to support additional use cases with a minor update to version 1.0.1.

Since its first release for public comment in May 2017, the working group has taken in feedback from the industry about use cases that need to be supported in the ads.txt mechanism. Released for public use in September 2017, Ads.txt version 1.0.1 is backwards compatible and has more details to support adoption in a wider range of use cases.

Updates in Ads.txt 1.0.1 are as follows:

  • File variable support, which allows publishers to list contact information (e.g. email address) in order for the public to contact the file owner,
  • Subdomain support, which clarifies that the ads.txt file on the root domain may include pointers to subdomains for more detailed ads.txt files,
  • Redirect support, which standardizes expected behavior for redirects outside the original root domain.

These updates in 1.0.1 should allow for greater adoption of ads.txt in the digital advertising industry, by supporting more publisher use cases.

Version history

Current version: 1.0.1

Previous version: 1.0

The specification can be found at