ads.txt
A public text file that declares which companies are authorized to sell a publisher's ad inventory.
What is ads.txt?
ads.txt (Authorized Digital Sellers) is an IAB Tech Lab initiative that allows publishers to publicly declare which companies are authorized to sell their digital ad inventory. It is a simple text file hosted at the root of the publisher's domain (e.g., example.com/ads.txt) that lists all authorized sellers along with their relationship type (direct or reseller) and account IDs.
The ads.txt standard was created to combat domain spoofing and unauthorized inventory reselling — forms of ad fraud where bad actors claim to sell inventory on premium publishers' domains without authorization. By checking a publisher's ads.txt file, DSPs and advertisers can verify that the seller offering inventory is actually authorized to sell it.
Why It Matters for Publishers
ads.txt is no longer optional — it is a critical requirement for programmatic monetization. Most major DSPs and ad buyers now filter out bid requests from sellers not listed in the publisher's ads.txt file. If your ads.txt is missing, incomplete, or incorrectly configured, you are losing significant programmatic demand and revenue.
A common issue is outdated ads.txt files. As publishers add or remove SSPs and demand partners, the ads.txt file must be updated to reflect current relationships. Stale entries for discontinued partners don't cause immediate harm but add clutter, while missing entries for active partners directly reduce demand.
Example
A typical ads.txt entry looks like:
google.com, pub-1234567890, DIRECT, f08c47fec0942fa0
This declares that Google (google.com) is authorized to sell inventory directly for the publisher's account (pub-1234567890), with an optional certification authority ID.
Best Practices
- Audit ads.txt monthly: Compare your ads.txt entries against your active demand partners. Remove entries for partners you no longer use and add entries for new partners.
- Use your SSPs' recommended entries: Each SSP provides specific ads.txt entries for your account. Use their exact recommended entries to avoid configuration errors.
- Validate your file: Use tools like ads.txt validators to check for formatting errors, duplicate entries, and missing required fields that could cause DSPs to ignore entries.
- Include all resellers: If your demand partners resell your inventory through other exchanges, include those reseller entries as well. Missing reseller entries can block significant demand.
- Monitor ads.txt crawl status: Check Google Ad Manager's ads.txt status to ensure Google is successfully crawling and parsing your file. Crawl errors can silently reduce your demand.