At The Green Web Foundation, we get a fair few people asking us “how can I improve the sustainability of my website?". In this series - A beginners guide to performing a website carbon audit - we set out to help folks get started along the path to answering that very question.

In this post (part one of the series), we’ll look at assessing the carbon emissions of website hosting. In parts two and three we’ll cover data transfer, and device energy usage respectively. You can find links to the other parts below:

Before starting, it’s worth noting that this series of posts is aimed at people/organisations looking to start understanding the carbon emission impact of their websites. They will help website owners uncover potential areas for improvement on their sites. They will not, however, be providing detailed carbon emission estimates based on actual usage, lifecycle analysis, or other measures that might be required for corporate reporting.

Introduction to hosting

Choosing a green web host for a website is one of the most impactful decisions any website owner can make. Based on peer-reviewed research, the Sustainable Web Design model says hosting accounts for 15% of a website’s total energy usage. Beyond making your own site more sustainable, it also sends a message to other hosting providers that their potential customers value services that are powered by renewable energy.

Checking how a site is hosted is also as good a place as any to start a website audit. For this audit, we’ll use the COP27 website ( Let’s get started.

Check if a site is on a green web host

The first thing we’ll do is check if the website uses a verified green hosting provider known green web host (or CDN - more on that later). At The Green Web Foundation, we maintain an open dataset of verified providers. We’ve also created a few user-friendly ways for people to check websites against that dataset.

Using the Green Web Checker online

One way to check a website against our dataset is to use the Green Web Checker tool online. Running the COP27 domain ( through this tool reveals that the site is not hosted on a known green providers or CDN.


Using the Greencheck API

For developers, or those looking to automate green hosting checks, we’ve also created the Greencheck API. You can use this API to check a single domain. Below is how we can use this API to check the COP27 domain.

curl -X 'GET' \\
 '<>' \\
 -H 'accept: application/json'

This returns the below response.

  "green": false,
  "url": "",
  "data": false

With this, we can check for the green key to know if a site is hosted on a green web host (true) or not (false). For green hosted sites, the API also returns additional information about the hosting provider.