A webservice hosting the api of the language model has to run on http://localhost:8080. To set up the webservice, see https://github.com/giganticode/vsc-extension-backend.
Run the 'run.bat'-script (Windows) or the 'run.sh'-script (UNIX). The script will install all dependencies and start a webserver. By default, the webservice starts at port 3000, so the web-tool can be under http://localhost:3000.