ads.txt and app-ads.txt: A Checklist for MCM Publishers

Ads.txt is one of the simplest files on your site and one of the easiest to get wrong. When you join an MCM program, it becomes even more important, because buyers check it to confirm that your partner is allowed to sell your inventory.

What these files are

• ads.txt (Authorized Digital Sellers) is an IAB standard that lets a website declare which companies may sell its ad inventory.
• app-ads.txt does the same for apps and is hosted on the developer website linked from the app's store listing.

Google describes both as optional but highly recommended. Their job is to protect you from counterfeit inventory, so that ad spend meant for you does not go to someone pretending to be you.

Where they live

• ads.txt sits at the root of your domain, for example example.com/ads.txt.
• app-ads.txt sits at the root of the developer domain listed in your app store page.

Both must be publicly reachable. Google notes the files must not be blocked by a geofence, and it publishes guidance on making sure they can be crawled.

Checklist when joining an MCM partner

1. Get the exact lines from your partner. Your MCM parent will tell you which seller lines to add. Copy them exactly.
2. Keep existing valid lines. Do not delete lines for demand partners you still use.
3. Remove stale lines. Old partners you no longer work with should come out.
4. Check the format. One entry per line: domain, account ID, relationship (DIRECT or RESELLER), and an optional certification ID.
5. Test the URL. Open it in a browser from a different network to confirm it loads as plain text.
6. Review status in Ad Manager. Google offers a page to review the authorization status of your domains. Use it after any change.

Common mistakes

• Hosting the file on a subdomain only, or behind a redirect that crawlers cannot follow.
• Uploading a rich-text file instead of plain text.
• Typos in publisher IDs.
• Forgetting app-ads.txt for apps and CTV apps.

Ad Manager can help

Ad Manager can generate ads.txt and app-ads.txt content based on your network's seller information, check file syntax and show which sellers are authorized for your inventory.

Why it matters for Holuron publishers

Holuron onboards websites, apps and CTV apps to AdX through MCM. Accurate authorization files help buyers trust that inventory and bid on it with confidence.

When your files are in order, what's left to check is the network itself. Apply for an account review to see whether it qualifies for Holuron's MCM program.