Ads.txt Technical Information

What is ads.txt?

The mission of the ads.txt project is simple: To increase transparency in the programmatic advertising ecosystem. Ads.txt stands for Authorised Digital Sellers and is a simple, flexible and secure method that publishers and authorised partners can use to publicly declare the companies they have sanctioned to sell their digital inventory.

IAB Australia supports local publishers adopting this solution as a method of helping to eliminate the ability of criminal entities profiting from counterfeit inventory in the open Australian digital advertising ecosystem. Once adopted at scale, buyers can use ads.txt files to shift media spend to authorised supply paths.

Towards the bottom of this page you’ll find open industry-wide support from key local advertising technology vendors. We are keen to support Australian media-owners on the viability and ease of adopting ads.txt, to ensure that we can achieve wide-scale adoption in Australia. The next step will be for us to provide an update on progress from both local sellers and buyers. Thereafter we will work with the IAB Tech Labs in New York to provide timelines for when we can expect a workable update for non-web environments (i.e. mobile apps), when we can expect the inclusion of a wider range of ad formats and guidelines on the forthcoming updates to the OpenRTB protocol (OpenRTB 3.0).

How does ads.txt work?

Ads.txt is a secure, text-file based mechanism for publishers and authorised partners to publicly declare the companies that they have sanctioned to sell their digital inventory. Publishers should post the "/ads.txt" file on their root domain and any subdomains as needed.

Similar to robots.txt, ads.txt is easy to update, making it flexible. The data required to populate the file is readily available in the OpenRTB protocol, making it simple to gather and target. As can publishers sell their inventory through a variety of sales channels, ads.txt supports the following types of supplier relationships:

Domain owners who sell on exchanges through their own accounts
Networks and sales houses who programmatically sell on behalf of domain owners
Content syndication partnerships where multiple authorised sellers represent the same inventory
Programmatic buyers can then crawl the web for publisher ads.txt files to create a list of authorised sellers for each participating publisher. Then programmatic buyers can create a filter to match their ads.txt list against the data provided in the OpenRTB bid request.

Example: publishes ads.txt on their web server listing three exchanges as authorised to sell their inventory, including’s seller account IDs within each of those exchanges.

#< SSP/Exchange Domain >, < SellerAccountID >, < PaymentsType >, < TAGID >, 12345, DIRECT, AEC242, 4536, DIRECT, 9675, RESELLER

Note: The seller’s Publisher.ID will be specified in the “SellerAccountID” field in the ads.txt.

A buyer receiving a bid request claiming to be can verify if the exchange and SellerAccountID matches the authorised sellers listed in file.

For more information and support:

The AppNexus ads.txt validator

Technical specifications for ads.txt from the IAB Tech Lab

Partner Interaction Guide for ads.txt from the IAB Tech Lab

A working example (from of ads.txt

Open source crawler (for buyers to use in automating aggregation of ads.txt files from publishers)

AppNexus industry support page:

PubMatic support documentation:

Google Help Centre ads.txt article:

SpotX ads.txt support and info page:

Bench Infographic - How ads.txt Makes Advertising Transparent:

For any further information, questions or feedback - please contact Jonas Jaanimagi by email at

Google fully supports ads.txt and we’re working to integrate ads.txt functionality into all our ads systems to make sure advertisers' spend reaches the intended publisher. We believe it's crucial to provide buyers and publishers with a clear and safe method to benefit from programmatic channels.

Rhys Williams

Director, DoubleClick, AUNZ, Google

AppNexus is fully committed to ensuring that publishers and their authorised partners are fairly compensated for their inventory, and that advertisers get what they pay for. That’s why we’re supporting the ads.txt initiative, which promises to add more trust and transparency to the online advertising ecosystem. We like ads.txt because it puts publishers in the driver’s seat and lets them tell all buyers where they can safely find their inventory without the aid of a third party.

Dylan McBride

Commercial Director, AppNexus Australia

We encourage everyone to adopt ads.txt. Premium publishers’ application of this simple piece of code will improve the quality of inventory and everyone in the industry, except the bad actors, will benefit.

Mitch Waters

General Manager, AU/NZ, The Trade Desk

Ads.txt is a simple, flexible and secure method that publishers and distributors can use to publicly declare the companies they authorize to sell their digital inventory. Buyers will be able to identify approved sellers for a participating publisher, understand a publisher’s relationship with an exchange, and to some extent, compute the number of hops involved, allowing brands to assess the true value and authenticity of each impression. New initiatives and products evolve with time and ads.txt is no different. It’s a great step in the right direction - at PubMatic, we see great potential in scaling this solution further to include supplementary seller information like authorized geos, channels, and more.

Judith Engel

Senior Director, APAC, PubMatic

SpotX employs a variety of methods and technologies to actively remove unauthorised traffic and to ensure buyers are accessing high-quality, brand-safe inventory. Ads.txt is one more tool in our fight against fraud in video advertising and we are working very closely with our publishers to ensure SpotX is appropriately listed as an authorised platform

Christopher Blok

Country Manager, ANZ, SpotX

IAB Australia is keen to reassure publishers that ads.txt is a painless and transparent solution to embrace. If we can achieve scale here in Australia, then we would hope to see a healthy uplift in local automated media buying against the verified domains that adopt this simple yet elegant solution.

Jonas Jaanimagi

Executive Consultant, IAB Australia

We wholeheartedly support the Ads.txt initiative as a key agent of change in support of the digital advertising industry’s move towards greater transparency. The eradication of shady media reselling and outright domain spoofing practices will bring brand spends and publisher revenues into closer alignment. With more of the advertising dollar hitting the pockets of our publishers, they will produce more of the engaging and inspiring content with which brands choose to align.

Steve Sullivan

Vice President, Compliance & Operations, Index Exchange

Ads.txt is a collaborative, industry-wide initiative endorsed by Rubicon Project, to help prevent unauthorised programmatic selling, and one that we have driven adoption for amongst our seller partners. Seller adoption of ads.txt is critical to cleaning up the ecosystem, and is a significant step towards our goal of building a trusted, safe, transparent ecosystem for buyers and sellers.

Simone Krakowiak

Country Manager, ANZ, Rubicon Project

We've been very impressed with IAB's ads.txt solution and how it aligns with Bench's vision of giving marketers full control over their multi-channel campaigns. It's a great initiative that promotes much-needed visibility across the programmatic supply chain and one that we're happy to lend our support to.

Gil Snir

Chief Commercial Officer, Bench

MediaMath is constantly updating the ways in which we protect our clients from fraudulent inventory. The IAB’s Ads.txt initiative is yet another tool that allows MediaMath to provide a brand safe environment for our marketers by eliminating counterfeited or ”spoofed” domains. We believe that this initiative will help both our buy side and sell side partners protect themselves against the bad actors that live within the supply chain.

Yun Yip

Country Manager, ANZ, MediaMath

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