Carbonalyser is a Firefox add-on designed to help users visualize the environmental impact of their internet browsing habits. By measuring data consumption, it calculates the electricity usage and greenhouse gas emissions associated with online activities. The add-on employs the '1byte' model developed by The Shift Project, allowing users to understand the hidden effects of digital technologies on climate change.

Key features include the ability to run and stop analyses of data traffic, reset measurements, and view a chart ranking the top websites by data usage. Users can also select their geographical location to refine emissions calculations based on local electricity sources. The results display a comprehensive overview of data generated, electricity consumed, and GHG emissions, providing comparisons with everyday activities such as smartphone charging and driving. Importantly, Carbonalyser ensures user privacy by processing all data locally.