Thank you for your comment @GeloBlueBrain. This script for Aseprite is not an extension and thus cannot be used as such. Try adding it as a script using the following steps:
- Extract the ZIP file
- Open Aseprite
- Go to File → Scripts → Open Scripts Folder
- Place the extracted files into the opened directory
- Restart Aseprite or reload the scripts folder
- Open the tool under File → Scripts → Write
Hope it helps :)