flask

Python web microframework CLI

TLDR

Run the development server

$ flask run

Run with debug mode and auto-reload

$ flask run --debug

Run on a specific host and port

$ flask run --host [0.0.0.0] --port [8080]

Start an interactive Python shell with app context

$ flask shell

List all routes in the application

$ flask routes

Initialize a database (if using Flask-Migrate)

$ flask db init

Run database migrations

$ flask db upgrade

Set the application module

$ FLASK_APP=[app.py] flask run

SYNOPSIS

flask [--app module] [--debug] command [options]

flask is the command-line interface for Flask, a popular Python web microframework. It provides commands for running development servers, opening application shells, and executing custom commands defined by Flask extensions or the application.
The CLI discovers the Flask application through the FLASK_APP environment variable or --app option. It supports loading from modules (app), module:app patterns (myapp:create_app()), or factory functions.
The development server (flask run) includes an auto-reloader that restarts when code changes and an interactive debugger that appears in the browser on errors. These features should only be used in development, never in production.
Flask extensions often add their own CLI commands. Flask-Migrate adds flask db commands for database migrations, Flask-Admin might add admin commands, etc. Applications can define custom commands using the @app.cli.command() decorator.
The shell command provides an interactive Python session with the application and its context pre-loaded, useful for testing and debugging.

PARAMETERS

--app module

Specify the Flask application module (or set FLASK_APP environment variable).

--debug / --no-debug

Enable/disable debug mode with auto-reloader and debugger.

run [--host host] [--port port]

Run the development server.

shell

Open an interactive Python shell with application context.

routes [--sort endpoint|methods|rule]

Show all registered URL rules.

--version

Show Flask version.

--help

Show help for a command.

RUN OPTIONS

--host address

Network interface to bind to (default: 127.0.0.1).

--port port

Port to listen on (default: 5000).

--reload / --no-reload

Enable/disable auto-reload on code changes.

--debugger / --no-debugger

Enable/disable the interactive debugger.

--cert path

SSL certificate file for HTTPS.

--key path

SSL key file for HTTPS.

CAVEATS

The development server is not suitable for production use. Debug mode exposes sensitive information and should never be enabled in production. The server is single-threaded by default. Use a production WSGI server like Gunicorn or uWSGI for deployment.

HISTORY

Flask was created by Armin Ronacher in 2010 as part of an April Fools' joke that became popular. The CLI was added in Flask 0.11 (2016), replacing the older flask-script extension and server startup method. Flask has become one of the most widely used Python web frameworks.