About this tool
ads.txt (and its app-ads.txt sibling) lets publishers declare which ad systems are authorised to sell their inventory. This tool builds a clean, valid file from your records, all in your browser with no upload.
Each line is "adSystemDomain, publisherID, relationship, [certAuthorityID]". The tool validates every row — the domain must look like a real domain, the publisher ID must be present, and the relationship must be DIRECT or RESELLER (case-insensitive) — then normalises the relationship to upper-case, removes exact duplicates, and passes comment lines (starting with #) through untouched. Rows that fail validation are counted and skipped rather than emitted.
Optional CONTACT= and SUBDOMAIN= directives can be added and accept several values separated by commas or new lines. A summary shows how many records were kept, deduped and skipped. Copy or download the result and host it at https://yoursite.com/ads.txt.