Flask 3 cheatsheet

Flask 3: Setup and CLI

7 common Flask 3 tasks.

Install Flask

Install Flask into the active virtual environment.

pip install flask

The smallest Flask application, saved as app.py.

from flask import Flask

app = Flask(__name__)

@app.get("/")
def index():
    return "Hello, World!"

Start the app with the debugger and auto-reload. Never use debug mode in production.

flask --app app run --debug

Listen on all interfaces on port 8000.

flask --app app run --host 0.0.0.0 --port 8000

Show all URL rules and their endpoints.

flask --app app routes

Start a Python shell with the application context active.

flask --app app shell

Add your own command, run with flask --app app seed.

@app.cli.command("seed")
def seed():
    """Load sample data."""
    print("Seeded")