The popular Jupyter Notebook bundle extension from Jupyter-contrib contains a spell checker. You can install and enable this (with admin privileges) like so:
pip install jupyter_contrib_nbextensions
jupyter contrib nbextension install --user
jupyter nbextension enable spellchecker/main
This may be the most popular spell checker for Jupyter Notebooks, but note that it simply highlights words not in its dictionary, and does not offer corrections.
If the extension installed properly, you will see this message in the command line:
Now, in the browser, after opening Jupyter, you will see the button labelled “abc” beside the keyboard button, which you can toggle to enable/disable spell check:
The jupyter-contrib library has many other useful modules such as code folding and table of contents.