The ads.txt specification was developed in the spring of 2017, covering desktop and mobile web inventory. Authorized Digital Sellers, or ads.txt is an IAB initiative that helps ensure that your digital ad inventory is only sold through sellers (such as AdSense) who you’ve identified as authorized. Creating your own ads.txt file gives you more control over who’s allowed to sell ads on your site and helps prevent counterfeit inventory from being presented to advertisers.

Why You Need Ads.txt

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We strongly recommend that you use an ads.txt file. It can help buyers identify counterfeit inventory and help you receive more advertiser spend that might have otherwise gone toward that counterfeit inventory.

Note: These instructions describe how to create an ads.txt file for Google publishers. Non-Google publishers should contact their SSP or exchanges.

Create your own ads.txt file for AdSense
Here’s how to create an ads.txt file to publicly declare that Google is authorized to sell your ad inventory:

  • Create a text (.txt) file.
  • Include the following line:
    google.com, pub-0000000000000000, DIRECT, f08c47fec0942fa0

Important: Make sure you replace pub-0000000000000000 with your own AdSense publisher ID.

  • Host your ads.txt file at the root level of your domain. (for example, https://example.com/ads.txt).
    Root levels are one level down from what’s listed in the public suffix list. For example, “yoursite.co.uk” is a root domain of “co.uk” but “maps.yoursite.co.uk” is not.

What information goes in an ads.txt file?
Create a text file named ads.txt and include separate lines for each exchange or SSP that is authorized to sell your inventory. Each of these lines should contain three pieces of data (plus a fourth optional field), in the format:

  • The canonical domain name of the system where bidders connect. This may be the operational domain of the system, if it’s different than the parent corporate domain, to facilitate WHOIS and reverse IP lookups to establish clear ownership. The SSP or exchange may publish the domain name to use.
    For Google seller accounts, the domain name is always google.com.
  • The publisher identifier associated with the seller or reseller account for the system in field #1. This must contain the same value as that specified in an SSP or exchange transaction (such as OpenRTB bid requests). Typically, in OpenRTB, this is the publisher.id field. For OpenDirect, it is typically the publisher’s organization ID.

For Google seller accounts, use the publisher ID displayed in each account (for example, pub-0000000000000000). To find this ID:

  • In AdSense: Sign in to your AdSense account and click Account and then Account information.
  • In Google Ad Manager: Sign in to Google Ad Manager and click Admin and then Global settings to find the publisher ID of your primary account and any other linked accounts.

Only include the pub- prefix and the 16-digit numeric code in your declaration. Delete the product-specific prefix (for example, ca- or ca-video-). If you monetize through multiple Ad Manager and/or AdSense accounts, you must include a separate row for each account, with its corresponding pub- code.

Domains hosting an ads.txt file where the seller’s publisher ID isn’t listed are no longer monetized through Ad Manager, and Google no longer buys ads on such sites. Updating your ads.txt files to include publisher IDs for each site you want to monetize is recommended. If you use Scaled Partner Management, we recommend working with your child partners to include your publisher ID in their ads.txt files.

  • The type of account or relationship. This field should be treated as case-insensitive when interpreting the data.
    • A value of ‘DIRECT’ indicates that the publisher (content owner) directly controls the account indicated in field #2 and has a direct business contract between the publisher and the advertising system.
      Google publishers who directly control the account indicated in field #2 should specify ‘DIRECT’.
    • A value of ‘RESELLER’ indicates that the publisher has authorized another entity to control the account indicated in field #2 and resell their ad space via the system in field #1.

Google publishers who don’t directly control the account indicated in field #2 should specify ‘RESELLER’. For example, an Ad Manager account using Scaled Partner Management should specify ‘RESELLER’ for inventory the account doesn’t directly manage.

  • (Optional): A unique identifier for the advertising system within a certification authority, which maps to the entity listed in field #1. One certification authority is the Trustworthy Accountability Group (TAG), and the TAG ID would be included here.
    For Google seller accounts, the TAG ID is f08c47fec0942fa0.

Frequently asked questions

I see an alert about my ads.txt file in AdSense. How do I check which of my sites has an incorrect ads.txt file?
If you see an ads.txt alert in your account, you can visit your Sites page to see a list of impacted sites.

How does Google enforce ads.txt files?
Google uses the content of any ads.txt files hosted on a root domain to determine which seller accounts are allowed to serve ads on that domain. No additional enforcement exists for root domains without an ads.txt file.

Google runs an auction and returns a winning ad for requests on sites where an ads.txt file exists with a correctly listed publisher identifier. If the identifier in the file is incorrect, an auction is not run for that request. New and updated ads.txt files are detected automatically, but changes may take up to 24 hours.

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What if the ads.txt file is hosted on a subdomain?
Google crawls and enforces ads.txt files placed on subdomains, where one exists, and is referenced from the ads.txt file on the root domain. The ads.txt management tool does not yet show a list of crawled subdomains.

Does Google support redirects?
Google supports a single HTTP redirect to a destination outside the original root domain (for example, example1.com/ads.txt re-directs to example2.com/ads.txt).

Multiple redirects are also supported, as long as each redirect location remains within the original root domain. For example:

  • example.com/ads.txt redirecting to www.example.com/ads.txt
  • example.com/ads.txt redirecting to subdomain.example.com/ads.txt
  • example.com/ads.txt redirecting to example.com/page/ads.txt

Ensure that your ads.txt files can be crawled
Once an ads.txt file is set up on your domain, the Google crawler will:

  • Attempt to crawl the file every 24 hours.
  • Parse the content of the file to determine seller IDs that are authorised to monetise your inventory.

To ensure that your ads.txt file can be crawled, Google recommends working through the following troubleshooting steps.

Confirm that the file isn’t temporarily unavailable
If a previously seen ads.txt file is unavailable on a subsequent re-crawl, the previously seen entries will be:

  • Purged if the response is a hard 404 error (page that actually doesn’t exist; HTTP 404 status).
  • Retained for up to five days if the response is a soft 404 error (a real page returned for a URL that doesn’t actually exist; HTTP 200 status) or a 500 server error.

Confirm that the file is reachable from the root domain
Redirects from domain.com/ads.txt to www.domain.com/ads.txt are fairly common. Ads.txt crawling will start at the root domain and the root domain needs to return from, or redirect to, the ads.txt file.

An ads.txt file on www.domain.com/ads.txt will only be crawled if domain.com/ads.txt redirects to it.

Ensure that crawling isn’t disallowed by robots.txt
The ads.txt file for a domain may be ignored by crawlers if the robots.txt file on a domain disallows one of the following:

  • The crawling of the URL path on which an ads.txt file is posted.
  • The User Agent of the crawler.

Example: Crawling disallowed on ads.txt file path

For example1.com:

  • An ads.txt file is posted on example1.com/ads.txt.
  • The following lines are included in example1.com/robots.txt:

User-agent: *
Disallow: /ads

  • The ads.txt file will be ignored by crawlers that respect the robots.txt standard.
  • You can modify the robots.txt file as follows to allow crawling of the file (other approaches are possible):
    • Option 1: Modify disallowed path.
      User-agent: *
      Disallow: /ads/
    • Option 2: Explicitly allow ads.txt; depends on crawler support for the Allow robots.txt directive.
      User-agent: *
      Allow: /ads.txt
      Disallow: /ads

Example: Crawling disallowed for User Agent
For example2.com:

  • An ads.txt file is posted on example2.com/ads.txt.
  • The following lines are included in example2.com/robots.txt:
    User-agent: Googlebot
    Disallow: /
  • The ads.txt file will be ignored by the Google crawler.

Ensure that the file is returned with an HTTP 200 OK status code
While a request for an ads.txt file may return the content of the file in the response body, if the status code in the response header indicates the file wasn’t found (e.g. status code 404):

  • The response will be ignored.
  • The file will be considered non-existent.

Make sure that the file has an HTTP 200 OK status code.

Ensure that there are no formatting errors or invalid characters in the file
Formatting errors, such as invalid whitespace characters, may be difficult to detect but can make an ads.txt file difficult to parse by a crawler and may therefore result in a file being ignored. Avoid copying and pasting ads.txt entries from a rich text editor; we recommend a plain text editor.

Make an ads.txt file reachable via both HTTP and HTTPS
The Google crawler attempts to crawl all ads.txt files on both HTTP and HTTPS. However, a 404 (or 40X) response causes previously crawled entries to be purged, even though an ads.txt file is crawled via HTTP. Therefore, if crawling via HTTPS returns a 404 (or 40X):

  • The previously crawled entry will be purged.

Please ensure that the ads.txt is accessible via both HTTP and HTTPS.

Ads.txt is a significant step in cleaning up bad inventory.

“It’s great to see adoption of ads.txt across the industry and we’re happy to see Google put their support behind this initiative. By eliminating counterfeit inventory from the ecosystem, marketers’ budgets will work that much harder and revenue will reach real working media to fund the independent, high-quality journalism which society depends upon.”

Anthony Hitchings, Digital Advertising Operations Director, Financial Times

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