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What Is ads.txt?

January 5th, 2021

It’s no secret that over the past several years the rate of fraud in the online advertising industry has increased significantly. With many organised ad fraud rings being discovered in recent years, fighting back against this rise in fraud has become a top priority for every advertiser.

To bring you up to date with the latest advancements in anti-fraud technology, we’re taking a look at a new anti-fraud measure: the ads.txt file.

Although it’s relatively new to the industry, it’s already had an enormous impact on the rate of fraud and has saved advertisers plenty of money.

In this article, we’ll be taking a look at what the ads.txt file is, and how it helps ad buyers protect their ad budget from criminals.

But before we take a closer look at the ads.txt file, let’s take a quick history lesson on how other .txt files have helped with similar problems in the past.

The History of .Txt Files

history of .txt file

If you’ve worked with computers for long enough, then a .txt file is pretty self-explanatory. Not only has it been around on computers for decades thanks to the likes of Notepad, but it’s also been an important part of many websites.

Currently, most websites will have a robots.txt file on their site that tells search engine crawlers such as Google and Bing which pages they can and can’t crawl. If a website doesn’t want a page or directory to appear in the Google search results, then they can simply add it to their robots.txt file.

This is incredibly useful if a website doesn’t want sensitive information showing up accidentally on search engines. The robots.txt file is always hosted on the root domain with the format domain/robots.txt (e.g.

You can try it yourself, go on any popular website and add /robots.txt to the end of the domain. The chances are you’ll be met with a blank looking page with a bit of text at the top, or an entire page of text like the robots.txt file from the Wall Street Journal below.

robots txt file

Each line in this robots.txt file tells search engines where they are not allowed to look. By limiting what a search engine can see, this gives site owners more control over their website and what shows up on Google.

Now you understand what .txt files can be used for on websites, you can probably guess how an ads.txt file is used too.

Similar to a robots.txt file, an ads.txt file is also hosted on the root domain of a website in the directory domain/ads.txt

Yet unlike the robots.txt file, the purpose of it is entirely different.

What Is ads.txt?

what is ads.txt

Introduced by the Interactive Advertising Bureau (IAB tech lab) in June of 2017, the ads.txt file is a list of authorised digital sellers (ADS) that are authorised to resell a publishers’ inventory.

Introduced to help combat the growing problem of domain spoofing in programmatic advertising, the primary goal of the file is to give buyers more confidence in the ads they purchase. Recently, a significant problem with programmatic ads has been the increase in fraudulent activity through fake domains and unauthorized reselling. This problem has become apparent with the discovery of large-scale fraud networks such as Methbot and Hyphbot which used counterfeit inventory to defraud advertisers out of millions.

Ads.txt is the response to this increase in unauthorized reselling and with implementation becoming more mainstream, this type of ad fraud could soon be wiped out entirely.

Usage On Sites

Any website can use an ads.txt file as long as they contain the correct information. Currently, the file must include the following information as outlined by the IAB tech lab:

  • The domain name of the advertising system or ad network
  • Publisher ID
  • Type of relationship
  • Type of inventory

An example of a line in an ads.txt file would look like the following:, 3713, DIRECT #display

In this example, the subdomain is an authorized seller of display ads from the website hosting the ads.txt file. The publisher ID for the subdomain is 3713 with a direct relationship with the site.

This usually means the relationship is direct and doesn’t involve any 3rd party exchanges or intermediaries. The final part of the entry is the type of inventory (ad) the website is using which is usually display, video or native.

All of this information is publically accessible by anyone who visits a website, allowing them to instantly see if another website has permission to display their ads. This becomes very helpful when fighting back against domain spoofing attacks where fake websites clone popular sites and try to sell their ad space.

Examples of ads.txt Files

Since the implementation of the ads.txt file, many major websites have started using it to protect themselves from online ad fraud. With the countermeasure being highly effective, it’s only a matter of time before every publisher will use it to protect their ad inventory.

To give you an idea of how other websites are taking advantage of the ads.txt file, here are some examples from some large and recognisable websites. Click the links below to view the full files and whitelisted websites.

Don’t forget to use the bullet points above for reference on what each section means.

What Are The Benefits of ads.txt?

With businesses losing billions of dollars to online fraud, the benefits of using ads.txt files are virtually endless. Not only is it super easy to install on any website, but it’s also easy to maintain while being exceptionally safe and secure.

To give you an idea of some of the major benefits ads.txt files give to website owners, here are just a select few of the most significant benefits.

Easy to Install

The ads.txt file is incredibly easy to install on websites. Just like the robots.txt file, webmasters can copy the file over to their root domain which can easily be accessed on any web browser from any device.

Safe and Secure

Unlike other ad prevention methods, the ads.txt file is exceptionally safe and secure. Since it can only be uploaded by the owner of the website, there is no way to edit the contents unless you have the correct permissions.

Easy to Edit

Publishers can quickly and easily edit their ads.txt files by simply re-uploading them to the root domain. This means if they need to add a new authorized digital seller to the list, it can be done so with minimal effort.

As you can see from the benefits above, the ads.txt file is simple to install, easy to use, and very secure. It’s no wonder organisations are pushing for it to become the new norm in programmatic advertising.

Protect Yourself From Unauthorized Sellers And Clicks

The ads.txt file is an excellent creation by the IAB tech lab to protect programmatic buyers and combat the rise in fraudulent activity. However, it only works when every publisher implements it on their sites and even then, it only protects programmatic ads. Other advertising networks such as Google Ads are still at risk from similar types of fraud such as the dreaded click fraud.

With hundreds of ads appearing on Google’s search engine, the ads.txt file won’t help advertisers protect themselves from repetitive clicks and invalid traffic. And if you opt to use Google display network, then your chances of receiving fraud is even higher.

To fight back against repetitive clicks that waste your money, you need specialist click fraud prevention software such as Lunio.

Compatible with all the popular types of Google ad types including display, search and shopping ads, Lunio automatically detects advertising fraud and takes action on your behalf. It’s like having your own personal bodyguard watching your ads.

To see how you can protect your Google Ads from fraudsters and annoying competitors, click below to sign up for a free 14-day trial.

Stop All Advertising Fraud in Seconds