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.py
   FastAPI   Starting development server 🚀

             Searching for package file structure from directories with
             __init__.py files
             Importing from /home/user/code/awesomeapp

    module   🐍 main.py

      code   Importing the FastAPI app object from the module with the
             following code:

             from main import app

       app   Using import string: main:app

    server   Server started at http://127.0.0.1:8000
    server   Documentation at http://127.0.0.1:8000/docs

       tip   Running in development mode, for production use:
             fastapi run

             Logs:

      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 [383138] using WatchFiles
      INFO   Started server process [383153]
      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.