An ads.txt file stands for “Authorized Digital Sellers” and is the latest tool in the online advertising industry’s fight against ad fraud. The purpose of ads.txt files is to allow advertisers and advertising networks to verify which entities are authorized to sell advertising on your website. This verification process is automated using “crawlers”, which are computer programs that index ads.txt files similar to a search engine. The information gathered is then used by advertisers and ad networks to automate the ad buying process.

Similar to a robots.txt file on your website, the ads.txt file is created at the root of your domain (e.g. https://yourdomain.com/ads.txt). This standard plain-text file contains a list of ad network domain names, each associated with an ID.

The format logically consists of:

1. An ads.txt file has a logical format, which consists of a non-empty set of records separated by line breaks. Each record contains a set of comma-separated fields, with three required fields and one optional field. The fields are formatted as: <FIELD #1>, <FIELD #2>, <FIELD #3>, <FIELD #4> or =.
2. Each record in an ads.txt file contains comma-separated fields, with three fields being required and one field being optional.
3. Comments can be included in an ads.txt file by starting a line with a hashtag. Any text after the hashtag will not be indexed by crawlers.
4. An ads.txt file may also contain contact information. If a website uses subdomains, the ads.txt file can reference these subdomains to notify crawlers that additional ads.txt files are present on these subdomains.
5. Starting from version 1.0.3, an ads.txt file can include inventorypartnerdomain - a reference to the domain of an entity that has explicit authorization to monetize ads within an application’s content. The corresponding appads.txt or ads.txt file of the partner will be hosted on this domain.

Example ads.txt file:

google.com, pub-770011223344550606, DIRECT, f08c47fec0942fa0
admixer.net, E1DF631C-1269-4EF3-A0FF-452A8B59DCB2, RESELLER
# An example comment
adtech.com, 11456, DIRECT #next comment
contact=support@windows10gadgets.pro
contact=https://windows10gadgets.pro/contact.html
subdomain=blog.domain.com
subdomain=news.domain.com
inventorypartnerdomain=programmerA.com
OWNERDOMAIN=mediacompany.com
MANAGERDOMAIN=bluemediamanager.com, US

The ads.txt specification specification requires that the records in an ads.txt file follow a defined structure, but the formatting of the file itself is not strict. This means that the presence or absence of spaces around comma delimiters, as well as white-space between records, will not affect how the ads.txt file is crawled. The file can be created using any text editor, on any computer operating system, just like any other text file.

Errors

Errors are serious issues which may invalidate your ads.txt file or cause lost revenue, they must be resolved immediately.

1. Incorrectly formatted data records and variables.
2. Invalid or incorrect exchange domains, publisher IDs, relationship values, and certification authority IDs.
3. Invalid lines which are not valid ads.txt records.

Warnings

Warnings highlight points of concern but which should not affect the processing of your ads.txt file, but which should be resolved as soon as possible.

1. Potentially invalid exchange domains.
2. Invalid variable names (not CONTACT, SUBDOMAIN, INVENTORYPARTNERDOMAIN, OWNERDOMAIN or MANAGERDOMAIN).
3. Invalid contact, subdomain, inventorypartnerdomain, ownerdomain and managerdomain variable values.
4. Duplicate ads.txt records detected (comments, including inline ones, are ignored).

Notices

Notices provide information on how to improve the formatting of your ads.txt file.

1. Inconsistent case and unnecessary whitespace.
2. Potentially incompatible comments containing unusual characters/symbols.
3. Missing certification authority IDs.