This is a very badly written Python script that uses the Todoist API to remove any unused tags (which isn't possible in bulk any other way, as far as I know).
It is my first working Python code and as such is very inefficient, but I will be improving it and hope to build on it to develop some other tools that are useful when dealing with Todoist (for example for analysis, sorting, etc.).
You need to add your Todoist API token to token.txt. Make sure there isn't any whitespace!
It should just work once you have done that.
This is highly unlikely to do anything unexpected as the API commands to delete tasks etc. just don't appear in the code, but don't blame me if it does. Everything is done at your own risk.
I may write this up on my website at some point when the code is better.