RaDMaX online is a major update to the previously published RaDMaX (radiation damage in materials analysed with X‐ray diffraction) software [Souilah, Boulle & Debelle (2016). J. Appl. Cryst.49, 311–316]. This program features a user‐friendly interface that allows retrieval of strain and disorder depth profiles in irradiated crystals from the simulation of X‐ray diffraction data recorded in symmetrical gθ/2gθ mode. As compared with its predecessor, RaDMaX online has been entirely rewritten in order to be able to run within a simple web browser, therefore avoiding the necessity to install any programming environment on the users' computers. The RaDMaX online web application is written in Python and developed within a Jupyter notebook implementing graphical widgets and interactive plots. RaDMaX online is free and open source and can be accessed on the internet at https://aboulle.github.io/RaDMaX‐online/.