🚀 Build a Todo App API with FastAPI + uv (The Cleanest Way!)

Source: Dev.to

Introduction

Want to build a lightning‑fast API without the Python packaging mess?
In this guide we’ll create a Todo API using FastAPI and uv, a next‑gen Python package manager that automates virtual environments, handles dependency resolution, and stays out of your way.

What is uv?

uv is a modern Python package manager that replaces pip and virtualenv with:

• 🚀 Ultra‑fast dependency installation
• 📦 Automatic virtual environment creation
• 🧼 Cleaner project setup with zero requirements.txt

Built in Rust, it’s ideal for fast, reproducible Python workflows—perfect for APIs, CLI tools, and data apps.

Project Setup

mkdir fastapi-todo && cd fastapi-todo
uv init --app
uv add fastapi --extra standard

Define the data model (models.py)

# models.py
from pydantic import BaseModel

class Todo(BaseModel):
    id: int
    title: str
    completed: bool = False

Build the FastAPI application (main.py)

# main.py
from fastapi import FastAPI, HTTPException
from models import Todo

app = FastAPI()
todos: list[Todo] = []

@app.get("/")
def home():
    return {"message": "Welcome to the FastAPI Todo App"}

@app.get("/todos")
def list_todos():
    return todos

@app.post("/todos", status_code=201)
def add_todo(todo: Todo):
    if any(t.id == todo.id for t in todos):
        raise HTTPException(status_code=400, detail="Todo with this ID already exists.")
    todos.append(todo)
    return todo

@app.put("/todos/{todo_id}")
def update(todo_id: int, updated: Todo):
    for i, t in enumerate(todos):
        if t.id == todo_id:
            todos[i] = updated
            return updated
    raise HTTPException(status_code=404, detail="Todo not found")

@app.delete("/todos/{todo_id}")
def delete(todo_id: int):
    global todos
    todos = [t for t in todos if t.id != todo_id]
    return {"message": "Todo deleted"}

Run the application

uv run fastapi dev

The server starts at http://127.0.0.1:8000.
Explore the interactive API docs at .