Understanding the Relation Between FastAPI and Uvicorn

If you’re coming from a JavaScript ecosystem (like I did) and are trying to develop apps in Python, you’ll likely find yourself comparing the components to better understand how they map across. Well, I’ve done that comparison for you — thank me later!

Let’s first take a look at the Python components and see how they compare to their JavaScript counterparts.

FastAPI and Uvicorn are two essential building blocks when developing high-performance Python APIs.

• FastAPI is the web framework. It helps you define routes, handle requests, perform validation, and build APIs easily. It follows the ASGI (Asynchronous Server Gateway Interface) standard.

• Uvicorn is the ASGI server. It is responsible for running your FastAPI app, handling incoming HTTP connections, and managing the event loop efficiently.

To illustrate this, think of FastAPI as the chef preparing the food (your API responses), and Uvicorn as the waiter delivering that food to the customer (handling requests and responses).

In simple terms:

FastAPI builds the application,
Uvicorn serves it to the world.

You develop your API with FastAPI, then use Uvicorn to launch it like this:

uvicorn main:app --reload

Here, main is your Python file, and app is your FastAPI instance. Together, FastAPI and Uvicorn enable you to build modern, fast, and scalable Python APIs with minimal effort.

Comparison