We've made some big updates to carbon.txt thanks to funding from NGI Search.
Learn more in this blog post

Implementing carbon.txt for your organisation

Organisations can use carbon.txt to link to information about their own sustainability-related disclosures, such as their carbon footprint, or the energy mix of the infrastructure they use, CSRD reports, or other similar information. This presents information in a manner that is both readable by humans and machines, and which can be subsequently verified by third parties.

In this guide, you will learn:

  • How to create a carbon.txt file for your organisation
  • How to upload your carbon.txt file to your servers
  • How to validate the contents of that carbon.txt file

  1. Create a carbon.txt file

    Follow the steps below to create a carbon.txt file for your organisation.

    • Use the carbon.txt builder

      The easiest way to create a carbon.txt file is to use the carbon.txt builder tool.

      The carbon.txt builder will help you create a carbon.txt file with the appropriate fields and content. You can then save the output in a carbon.txt file, or manually copy it and save it to a file on your computer.

      Use the carbon.txt builder

    • Manually create a carbon.txt file

      If you prefer to create the carbon.txt file manually, based on the latest syntax, in your favourite text editor.

      At a minimum, a valid carbon.txt file should contain at least one (1) publicly accessible link to an organisational disclosure document.

      Learn more about the carbon.txt syntax

  2. Upload your carbon.txt file

    Upload the carbon.txt file you just created to your website. We strongly recommend that you upload the file to the root of your domain - that is the URL should look something like this: https://www.my-org.com/carbon.txt.

  3. Validate your carbon.txt file

    Once you have uploaded your carbon.txt file, you can validate it using the carbon.txt validator. The validator will check that your carbon.txt file is correctly formatted and contains the required fields. It will also display the content of the carbon.txt file in a human readable format.

    Use the carbon.txt validator

Advanced

Linking a carbon.txt file to multiple domains

It's fairly common that a digital service provider might own and provide services through multiple domains. They might also have multiple products, or provide hosted services for a number of users all who have their own domains.

In this case, you can maintain a single carbon.txt file at one domain (e.g. https://my-org.com/carbon.txt) and refer other domains to that single source of truth.

There are two supported ways to do this:

  • Using DNS TXT records, which contain the specific URL pointing to the carbon.txt file to read.
  • Using a dedicated HTTP Via Header, again containing a URL for the carbon.txt file to read.

Choosing the right option for your organisation

Using DNS TXT records

Using DNS TXT records is intended for organisations who are able to add DNS records to both their own domain, as well as the domain they want to show up as green. If you own both domains, this option is for you.

Guide: How to link multiple domains using DNS TXT records

Using HTTP Via Header

Using a HTTP Via Header is intended for organisations who are not able to add DNS records for the domain they want to show up as green, but do accept HTTP requests for the domain, and serve responses for it. If you operate a CDN, a managed Wordpress service, or a general Platform-As-A-Service (PaaS) offering, this is usually better suited for your use case.

This option also allows you to "pass down" green claims to customer who use your service.

Guide: How to link multiple domains using HTTP VIA HEADER