FastAPI CLI

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FastAPI CLI is a command line program that you can use to serve your FastAPI app, manage your FastAPI project, and more.

When you install FastAPI (e.g. with pip install "fastapi[standard]"), it includes a package called fastapi-cli, this package provides the fastapi command in the terminal.

To run your FastAPI app for development, you can use the fastapi dev command:

fast →fastapi dev main.pyINFO     Using path main.py
INFO     Resolved absolute path /home/user/code/awesomeapp/main.py
INFO     Searching for package file structure from directories with __init__.py files
INFO     Importing from /home/user/code/awesomeapp

 ╭─ Python module file ─╮
 │                      │
 │  🐍 main.py          │
 │                      │
 ╰──────────────────────╯

INFO     Importing module main
INFO     Found importable FastAPI app

 ╭─ Importable FastAPI app ─╮
 │                          │
 │  from main import app    │
 │                          │
 ╰──────────────────────────╯

INFO     Using import string main:app

 ╭────────── FastAPI CLI - Development mode ───────────╮
 │                                                     │
 │  Serving at: http://127.0.0.1:8000                  │
 │                                                     │
 │  API docs: http://127.0.0.1:8000/docs               │
 │                                                     │
 │  Running in development mode, for production use:   │
 │                                                     │
 │  fastapi run                                        │
 │                                                     │
 ╰─────────────────────────────────────────────────────╯

INFO:     Will watch for changes in these directories: ['/home/user/code/awesomeapp']
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [2265862] using WatchFiles
INFO:     Started server process [2265873]
INFO:     Waiting for application startup.
INFO:     Application startup complete.

restart ↻

The command line program called fastapi is FastAPI CLI.

FastAPI CLI takes the path to your Python program (e.g. main.py) and automatically detects the FastAPI instance (commonly named app), determines the correct import process, and then serves it.

For production you would use fastapi run instead. 🚀

Internally, FastAPI CLI uses Uvicorn, a high-performance, production-ready, ASGI server. 😎

fastapi dev

Running fastapi dev initiates development mode.

By default, auto-reload is enabled, automatically reloading the server when you make changes to your code. This is resource-intensive and could be less stable than when it's disabled. You should only use it for development. It also listens on the IP address 127.0.0.1, which is the IP for your machine to communicate with itself alone (localhost).

fastapi run

Executing fastapi run starts FastAPI in production mode by default.

By default, auto-reload is disabled. It also listens on the IP address 0.0.0.0, which means all the available IP addresses, this way it will be publicly accessible to anyone that can communicate with the machine. This is how you would normally run it in production, for example, in a container.

In most cases you would (and should) have a "termination proxy" handling HTTPS for you on top, this will depend on how you deploy your application, your provider might do this for you, or you might need to set it up yourself.

Tip

You can learn more about it in the deployment documentation.