Flask includes a CLI (built on Click) that makes development workflows smooth.

How the Flask CLI finds your app

The CLI needs to know what Flask application to run.

Common ways:

• FLASK_APP=appFLASK_APP=app (points to app.pyapp.py module)
• FLASK_APP=package:create_appFLASK_APP=package:create_app (factory pattern)

Example

If you have app.pyapp.py with app = Flask(__name__)app = Flask(__name__):

export FLASK_APP=app
flask run

export FLASK_APP=app
flask run

Useful built-in commands

• flask runflask run — run dev server
• flask routesflask routes — list all routes (very helpful!)
• flask shellflask shell — open a Python shell with app context (commonly used in bigger apps)

Adding custom commands (preview)

Later, you can add custom commands like:

• flask create-adminflask create-admin
• flask seed-dbflask seed-db

Typically you’ll register them through the app factory or extensions.

Troubleshooting

If you see errors like:

• “Could not locate a Flask application”

It usually means:

• FLASK_APPFLASK_APP is not set
• your import path is wrong
• you’re in the wrong working directory