ads.txt Checker

ads.txt stands for "Authorized Digital Sellers." It is a plain text file that lives at the root of your domain — yoursite.com/ads.txt — and it lists, line by line, every advertising company allowed to sell inventory on your site. Buyers check that file before they bid. If your domain shows up in an ad exchange but your ads.txt does not name the seller offering it, the buyer assumes the inventory is spoofed and refuses to bid.

For a small publisher this shows up as quietly lower revenue rather than a broken page, which is why it goes unnoticed for months. Google AdSense specifically warns inside your account when the file is missing or does not contain your publisher ID, and unresolved warnings can limit which advertisers are willing to buy your impressions.

A healthy AdSense line looks exactly like this: google.com, pub-0000000000000000, DIRECT, f08c47fec0942fa0. Four fields, comma separated. The first is the exchange domain, the second is your publisher ID, the third is DIRECT if you own the account or RESELLER if a network sells on your behalf, and the fourth is the exchange's certification authority ID.

The failures we see most often are simple. The file is served with a 404 because it was uploaded into a subfolder instead of the web root. The file returns HTML because the hosting platform sends the 404 page with a 200 status. The publisher ID has a typo, or still says pub-XXXX from a copied template. The file sits on www but the site canonicalises to the bare domain, so crawlers following the canonical never see it. Fix the file, wait twenty-four hours for the exchange to re-crawl it, then re-run this check.