ads.txt, app-ads.txt and sellers.json for MCM Publishers

Buyers want proof that the company selling an impression is allowed to sell it. Three small files provide that proof, and in an MCM setup, getting them right is one of the first things your parent network will check.

The three files

• ads.txt sits at the root of your website and lists every company authorized to sell your web inventory.
• app-ads.txt does the same for apps. It lives on the developer website listed in the app store.
• sellers.json is published by the seller side (for example a parent network or exchange) and lists the companies it sells for, so buyers can match both ends of the chain.

Ad Manager can generate the right lines for your network and validate the syntax for you, as explained in Google's guide on creating and submitting ads.txt or app-ads.txt.

What MCM adds

Google's setup guidance for MCM child publishers lays out four pieces that have to line up:

1. The child's ads.txt or app-ads.txt must list the parent as an authorized seller with the relationship marked DIRECT, not RESELLER.
2. The parent adds the child's seller details to its own files.
3. The child opts in to sellers.json listing and provides a business domain in Ad Manager, a setting covered in Google's sellers.json listing and business domain help.
4. The parent's sellers.json lists the child as a Publisher (or Both), using the Seller ID field Google documents in its sellers.json and Seller ID guide.

The same setup page also asks child publishers to update ads.txt with the Ad Exchange code shown in their network settings once sites are approved.

Common errors and fixes

Diagnostic	What it means	Fix
NO_ADS_TXT	File missing or unreadable	Publish the file at the domain root and confirm it loads
Wrong seller type	Line marked RESELLER	Change the parent's line to DIRECT
SELLER_MISSING	Child not in parent's sellers.json	Ask the parent to add you
BUSINESS_DOMAIN_NOT_PROVIDED	No business domain in Ad Manager	Add it in your network settings

This table matches the error names in Google's MCM diagnostics reference, which also notes that changes can take up to 48 hours to show after you republish.

Good habits

• Keep one person responsible for ads.txt edits
• Remove lines for partners you no longer work with
• Check the file loads over HTTPS without redirects to other domains
• For apps, confirm the developer URL in the store matches the domain hosting app-ads.txt

How H&T GAMING uses it

H&T GAMING lists ads.txt enforcement and sellers.json transparency among its compliance checks, so expect these files to be reviewed during onboarding.

If you are not sure your ads.txt and sellers.json lines are set up correctly, you can request a free account review and have them checked before they cost you demand.