SWAN (Service for Web-based ANalysis) is a CERN service that allows users to perform interactive data analysis in the cloud, following a "software as a service" model. It is built upon the widely-used Jupyter notebooks, which allows users to write - and run - their data analyses using only a web browser. Moreover, by connecting to SWAN, users have immediate access to the CERN storage, software and computing resources they need to do their analyses.