1. Initialize the Project#

First, I created the project structure. uv handles the creation of the pyproject.toml. Then I created the virtual environment with uv venv.

uv init my-fastapi-app
cd my-fastapi-app
uv venv

2. Add Dependencies#

Next, I added FastAPI and Uvicorn (the ASGI server).

uv add fastapi uvicorn

Observation: The installation was nearly instantaneous. uv caches aggressively, making this step much smoother than standard pip.

3. The “Hello World” Code#

I created a simple main.py file to verify the installation:

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello World"}

4. Running the API#

To start the development server with “hot reload” (so it updates whenever I save the file), I ran:

uv run uvicorn main:app --reload

1. Project Initialization#

Starting a new project from scratch.

• uv init: Initializes a new project with a pyproject.toml.
• uv venv: (Optional) Manually create a virtual environment, though uv run handles this automatically.

2. Managing Dependencies#

This is what you will use most often as you add libraries like Pydantic, SQLAlchemy, or Jose (for JWT).

• uv add fastapi uvicorn: Adds dependencies to your project and installs them.
• uv add --dev pytest: Adds a package only for development/testing.
• uv remove <package>: Removes a dependency.
• uv tree: Visualizes your dependency graph (great for seeing what FastAPI relies on).

3. Running Your Application#

You don’t need to “activate” environments manually if you use uv run.

• uv run uvicorn main:app --reload: Runs your FastAPI app in the managed environment.
• uv run python script.py: Runs a specific Python script using project dependencies.

4. Environment & Python Versions#

• uv python install 3.12: Installs a specific Python version if you don’t have it.
• uv sync: Ensures your lockfile and environment are perfectly aligned.