What is an API?
An API (Application Programming Interface) is like a waiter at a restaurant—it takes your order (request), tells the kitchen (server) what you want, and brings you back food (response).
With FastAPI, you can build a web API in Python that other programs (or websites) can talk to.
Set up a FastAPI project
In your terminal, create a new folder and install FastAPI:
mkdir -p python-tutorials/fastapi-hello
cd python-tutorials/fastapi-hello
uv venv
uv pip install fastapi uvicorn
fastapi is the framework, and uvicorn runs the server.
Your First API
Create a file main.py:
from fastapi import FastAPI
app = FastAPI()
@app.get("/")
def read_root():
return {"message": "Hello, World!"}
@app.get("/hello/{name}")
def greet(name: str):
return {"message": f"Hello, {name}!"}This creates two endpoints:
/— says "Hello, World!"/hello/YourName— greets you by name
Run the API
Start the server:
uv run uvicorn main:app --reload
Open http://127.0.0.1:8000 in your browser—you'll see the JSON response.
Try http://127.0.0.1:8000/hello/Alice to see a personalized greeting.
Explore the docs
FastAPI auto-generates documentation. Visit http://127.0.0.1:8000/docs to test your API interactively.
What's Next?
In the next tutorial, you'll add a local NoSQL database and build an API for a simple store.