# python manage.py debug
* Serving Flask app "server/__init__.py"
* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
* Debug mode: on
Then raising an error in Firefox yields
Internal Server Error
The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.
This used to work at some point, but now it isn't.
FLASK_DEBUG = true or 1, does not work
FLASK_ENV = development, does not work