Let's look at the AMSCO cipher. This is a positional cipher with exchanges. You can easily encode or decode a message with a pen and paper, that is of course, if you know the key.
The key is represented as a number that consist of unique digits from 1 to N. N is a length of the key. To encode message we should write a message in a matrix with N columns. The matrix is written row by row. In this process, one or two characters are alternately recorded in a field. One or two characters alternate in rows and in columns too (like...
CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.
In order to install CheckiO client you'll need installed Python (version at least 3.8)
Install CheckiO Client first:
pip3 install checkio_client
Configure your tool
checkio --domain=py config --key=
Sync solutions into your local folder
(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)
checkio serv -d
Alternatevly, you can install Chrome extension or FF addon
checkio install-plugin --ff
checkio install-plugin --chromium