For past users of Mathematica’s now defunct CDF plugin, MathCell provides the functionality of the
The other major motivation for development is to avoid reliance on any server-based online services. MathCell runs entirely in the browser and does not require external servers to function. That means it can be used in the place of Jupyter/IPython widgets in stand-alone web pages, thereby avoiding the server-side rendering of notebooks. It also provides the functionality of SageMathCell interacts without the server-side processing delay.