Write an ads.txt file that ad systems can actually read

One malformed line can make a whole ads.txt unreadable to crawlers. The format is four comma-separated fields — here is how to assemble it without the usual mistakes.

Tools used in this guide

The job

ads.txt tells ad systems which accounts are allowed to sell your inventory. Each line is one authorized seller: the ad system's domain, your account id there, and DIRECT (you have a contract) or RESELLER (a third party sells for you). An optional fourth field carries the certification authority id — for Google that is the TAG id f08c47fec0942fa0.

Assemble the lines

Enter one record per line and generate. Optional declarations go at the top of the file: OWNERDOMAIN= for the owning entity, CONTACT= for a reachable address, MANAGERDOMAIN= when an agent manages your inventory, SUBDOMAIN= and INVENTORYPARTNERDOMAIN= where the spec asks for them.

DIRECT vs RESELLER is about your contract, not how the code loads — check your ad system's own docs for which to use.
Field order and the comma separators are fixed; a stray space or a fifth field breaks the line.
The checker mode flags bad domains, wrong relationships, empty fields and unknown declarations line by line — run your existing file through it before editing.

Deploy and limits

The finished file goes at your domain root as /ads.txt — for an app it is app-ads.txt on the developer site the store listing points to. This tool assembles spec-shaped lines; it does not check that the account ids exist at each system, and a valid file is not an approval or revenue guarantee.