# fastapi > Run FastAPI apps which uses Uvicorn under the hood. > More information: . - Run a FastAPI app with automatic reload (for development): `fastapi run {{path/to/file.py}} --reload` - Serve your app in both development mode: `fastapi dev {{path/to/file.py}}` - Specify the host and port to run on: `fastapi run {{path/to/file.py}} --host {{host_address}} --port {{port}}` - Set the app variable name (if not `app`) or specify a custom app directory: `fastapi run {{path/to/file.py}} --app-dir {{path/to/app}} --app {{custom_app_name}}` - Display help: `fastapi --help` - Display help for a subcommand: `fastapi {{subcommand}} --help`