ads.txt is a plain text file that takes five minutes to create, yet a missing or broken one can stop buyers from bidding on your inventory. This guide shows exactly what goes in the file, where to put it, how sellers.json fits in, and how to fix the errors publishers run into most often.
What is ads.txt and why does it matter?
ads.txt ("Authorized Digital Sellers") is a standard from IAB Tech Lab. It is a public file at the root of your domain, for example https://example.com/ads.txt, listing every company you allow to sell your ad inventory.
It exists because of domain spoofing: bad actors used to pretend to sell ads on well-known websites they had nothing to do with. Today most programmatic buyers crawl ads.txt files and check every bid request against them. If the seller in the request is not listed in your file, many buyers will not bid. In practice, no valid ads.txt often means lower demand and lower fill.
The ads.txt line format
Each authorised seller is one line with up to four comma-separated fields:
<advertising system domain>, <your publisher account ID>, <DIRECT or RESELLER>, <certification authority ID (optional)>- Advertising system domain: the canonical domain of the SSP or exchange, for example
msadsnetwork.com. - Publisher account ID: the ID that platform assigned to you or to the seller account. It must match the ID used in bid requests exactly.
- Relationship:
DIRECTif you control the account yourself;RESELLERif another company sells your inventory through its own account. - Certification authority ID: an optional TAG ID for the advertising system. Only add it if the platform gives you one.
The MS Ads Network ads.txt itself contains this line for our own seller account:
msadsnetwork.com, msads-ssp-001, DIRECTYour dashboard shows the exact line or lines for your own account. Always copy them from there instead of typing them by hand.
You can also add two optional variables: OWNERDOMAIN= (the business domain that owns the site) and MANAGERDOMAIN= (a company that manages your monetization). Lines starting with # are comments.
How to create and upload ads.txt
- Collect your lines. Each platform you work with (SSPs, AdSense, networks) gives you its own line or lines. Keep them all; ads.txt is a list, not a single entry.
- Create a plain text file named
ads.txtin a plain text editor. Save it as UTF-8 without formatting. Word processors can add hidden characters. - Upload it to the root of your domain, so it opens at
https://yourdomain.com/ads.txt, not in a subfolder. - Check it in a browser. You should see plain text, not an HTML page, a download prompt or a redirect to a login page.
- Tell your platforms. Many dashboards, including ours, re-check your file automatically and show whether your line was found.
WordPress
You can upload the file through your hosting file manager or FTP into the folder that contains wp-config.php. Some SEO and ad plugins can also manage ads.txt; use one method only so they do not overwrite each other.
Blogger, Wix and other hosted platforms
Hosted builders usually offer an ads.txt setting in the monetization or SEO section of the dashboard, because you cannot upload files directly. Paste all your lines there.
Subdomains
Buyers look for ads.txt on the root domain. If your site lives on a subdomain, the root domain's file can point to it with a subdomain= line. Follow your platform's instructions in that case.
How sellers.json fits in
ads.txt is the publisher's side of the story: "these companies may sell my inventory." sellers.json is the platform's side: a public file where an SSP or exchange lists the sellers it represents, with their seller IDs and whether each is a publisher or an intermediary. Ours is at https://msadsnetwork.com/sellers.json.
Buyers combine the two. They take the account ID from a bid request, look it up in the platform's sellers.json to see who the seller is, and check the publisher's ads.txt to confirm the seller is authorised. A third standard, the SupplyChain object, carries the full path of a request when several companies are involved. Together they make the supply chain verifiable from end to end.
You do not edit sellers.json yourself. You just make sure the ID in your ads.txt is the same one the platform lists for you.
Common ads.txt errors and how to fix them
| Problem | Typical cause | Fix |
|---|---|---|
| File returns 404 | Uploaded to a subfolder or the wrong site | Move it to the web root so /ads.txt opens directly |
| Shows an HTML page | A CMS or redirect catches the URL | Serve it as a static file with Content-Type: text/plain |
| Line "not found" in dashboard | Typo, extra spaces or wrong ID | Copy the line from the dashboard again; check for curly quotes or hidden characters |
| Other networks' lines disappeared | A plugin or new upload overwrote the file | Keep a master copy; merge all lines into one file |
| Redirects to another domain | HTTP→HTTPS or www rules | Redirects within the same domain are fine. Avoid redirects to a different domain |
| Changes not visible | Caching or crawler delay | Clear your site cache; buyers re-crawl periodically, so allow a day or two |
Keep it tidy
- Remove lines for platforms you no longer use, so old resellers cannot sell your inventory.
- Review the file whenever you add or drop an ad partner.
- Keep one master copy outside your website so you can restore it quickly.
- For mobile apps, publish
app-ads.txton the developer website listed in your app store page; the format is the same.
Frequently asked questions
Is ads.txt required?
It is not a law, but in practice most programmatic buyers rely on it, and many platforms (including MS Ads Network) require the correct line before serving ads to your site.
Can I list more than one platform?
Yes. ads.txt is meant to list every authorised seller. Add every line each platform gives you.
How long until a new ads.txt is recognised?
Platforms and buyers crawl on their own schedules. Many pick changes up within a day, but allow a few days before troubleshooting further.
Does ads.txt affect SEO?
It is not a search-ranking factor. It affects which advertisers are willing to buy your inventory.
Set up ads.txt with MS Ads Network
After you add your site, your dashboard shows the exact ads.txt line and checks it for you. New to the terms? See the ad tech glossary or read what an SSP is.
Create a publisher account