These widgets are designed to support image analysis with the Insight Toolkit (ITK), but they also work with other spatial analysis tools in the scientific Python ecosystem, such as scipy.ndimage, scikit-image, ImageJ-ImgLib2, Dask, OpenCV, or the Visualization Toolkit (VTK), thanks to ITK's NumPy interoperability layer. These widgets are powered by itk.js and vtk.js, JavaScript and WebAssembly interfaces and implementations of ITK and VTK. The package is open source, licensed with the Apache 2.0 license, and developed with the SciPy community. Matthew McCormick, Sebastien Jourdain, Ken Martin, Jean-Christophe Fillion-Robin and Alexis Girault