Key Takeaways

• Ads.txt is a simple text file that publishers add to their website root directory to list authorized ad sellers

• It helps prevent ad fraud by stopping unauthorized parties from selling fake inventory

• Implementation is straightforward but requires regular maintenance

• Most major ad platforms now expect websites to have a valid ads.txt file

• Without it, publishers may lose significant revenue from premium advertisers

What's Ads.txt, and Why Should You Care?

If you've spent any time trying to monetize a website with display ads, you've probably heard about ads.txt. But what exactly is this mysterious file, and why do ad networks keep insisting you need one?

Ads.txt (Authorized Digital Sellers) is basically a text file that site owners place on their domains to publicly declare which companies are allowed to sell their ad inventory. Think of it as a guest list for your website's advertising space - only those on the list get to sell your ads.

The Interactive Advertising Bureau (IAB) Tech Lab created this standard back in 2017 to fight the growing problem of counterfeit inventory and domain spoofing in programmatic advertising. Before ads.txt, sketchy middlemen could pretend to sell ad space on premium websites they had no relationship with, pocketing the money while showing ads on low-quality sites instead.

How Ads.txt Works

The beauty of ads.txt is its simplicity. It's just a plain text file that lives at the root of your domain (like example.com/ads.txt) and contains a list of entries that look like this:

Each line contains four pieces of information:

1. The domain name of the ad system (like Google AdSense)

2. Your publisher ID with that system

3. The relationship type (DIRECT or RESELLER)

4. An optional certification ID

When an advertiser wants to buy inventory on your site through programmatic channels, their systems check your ads.txt file first. If the seller isn't listed there, the buy doesn't happen. This simple verification prevents fraudsters from impersonating your site.

Why Implement Ads.txt?

There are some real benefits to implementing ads.txt on your site:

1. Fight Ad Fraud: You prevent bad actors from pretending to sell your inventory

2. Increase Revenue: Many premium advertisers and DSPs (demand-side platforms) refuse to buy inventory that isn't ads.txt verified

3. Build Trust: Shows advertisers you're serious about maintaining a quality advertising environment

4. Industry Standard: It's now considered a basic requirement for professional publishers

According to Setupad, publishers without a proper ads.txt file can lose access to significant demand sources, potentially reducing their ad revenue by 10-30%.

Common Implementation Mistakes

While ads.txt is a straightforward concept, publishers often make mistakes that limit its effectiveness:

1. Outdated entries: Adding partners but never removing them when relationships end

2. Copy-paste errors: Typos in domains or publisher IDs make entries useless

3. Overloaded files: Having too many RESELLER entries can raise red flags with DSPs

4. Invalid syntax: Each entry must follow the exact format and be on a single line

5. Missing file verification: Not checking that the file is actually accessible

As Sellers.guide notes, many publishers "don't maintain it or validate new sellers' lines before adding them to the file, practically exposing themselves to fraud and malpractice."

Ads.txt vs. App-ads.txt vs. Sellers.json

Ads.txt is just one piece of the transparency puzzle in digital advertising. There are now related standards you should know about:

• App-ads.txt: The mobile app version of ads.txt, used for in-app advertising. It works similar to website ads.txt but is implemented differently since apps don't have web domains.

• Sellers.json: This is like ads.txt but from the other direction. While ads.txt is on publishers' sites listing authorized sellers, sellers.json is on the ad platforms' domains listing all the publishers they're authorized to sell for.

Together, these standards create a more transparent advertising ecosystem where buyers can verify sellers, and sellers can verify publishers.

Getting Started with Ads.txt

Ready to implement ads.txt? Here's a simple guide:

1. Gather information: Contact each of your ad partners (AdSense, other networks, etc.) and ask for their ads.txt lines

2. Create your file: Use a plain text editor to create a file named "ads.txt"

3. Add valid entries: Include all authorized partners, one per line

4. Upload the file: Place it in the root directory of your domain

5. Verify it works: Visit yourdomain.com/ads.txt to make sure it's accessible

6. Set a maintenance schedule: Review your file quarterly to remove outdated entries

According to Primis, "When creating an ads.txt file, it's important to only include the direct partners that you work with or their verified resellers."

Final Thoughts

Ads.txt isn't just another technical requirement – it's a simple way to protect your ad inventory and ensure you're getting paid fairly for the audience you've built. While implementation isn't difficult, maintaining an accurate ads.txt file requires ongoing attention.

For most publishers, the small effort of creating and maintaining an ads.txt file pays off with increased advertiser trust, higher fill rates, and better overall ad revenue.