ads.txt explained: setup, validation, and common mistakes

ads.txt (Authorized Digital Sellers) is an IAB standard that lets publishers publicly declare which companies can sell their inventory. Missing or invalid ads.txt files cause "Earnings at risk" warnings inside AdSense.

adSystemDomain, publisherId, relationship, certificationAuthorityId

For AdSense:

google.com, pub-0000000000000000, DIRECT, f08c47fec0942fa0

The file must be served as plain text at https://yourdomain.com/ads.txt — the root, not a subdirectory.

• Wrong content type (HTML instead of text/plain).
• Using the wrong publisher ID format (missing pub- prefix).
• Duplicate lines.
• Hosting on subdomains without separate ads.txt for each.

Run our free ads.txt validator to fetch and parse yours line-by-line.