One day, the internet will be powered by renewable energy. Until that day comes, there’ll be a CO2 cost that comes with every byte of data that’s uploaded, downloaded or stored. By being able to calculate these emissions, developers can be empowered to create more efficient, lower carbon apps, websites, and software.
What is CO2.js?
CO2.js is an open-source JavaScript library that enables developers to estimate the emissions related to use of their apps, websites, and software.

Curious about driving the transition to a fossil-free internet? Here’s how CO2.js can help.
This article goes in depth about the concepts behind CO2.js, it’s uses, and when other tools might be better options to consider.
How to use it
CO2.js can be quickly installed into JavaScript projects using NPM. Other installation options can be found on our documentation website – CO2.js: Installation.
Resources for developers

CO2.js recent release notes
Case studies
Here’s a few stories of how companies and individuals in are using CO2.js in real world applications today.
If you’re using CO2.js in production we’d love to hear how! Drop us a line.
Sitespeed.io – Using and contributing to CO2.js
Sitespeed.io is an open-source website performance monitoring solution that also has a sustainability plugin powered by CO2.js.
Licenses
The code for CO2.js is licensed Apache 2.0 (What does this mean?).
The average carbon intensity data from Ember is published under the Creative Commons ShareAlike Attribution Licence (CC BY-SA 4.0). (What does this mean?)
The marginal intensity data is published by the Green Web Foundation, under the Creative Commons ShareAlike Attribution Licence (CC BY-SA 4.0). (What does this mean?)