fastapi

FastAPI

Official FastAPI skill to write code with best practices, keeping up to date with new versions and features.

Project note: This project starts the server via ./run_services.sh (uvicorn), not fastapi dev. The patterns below still apply to all endpoint/model code.

Use the fastapi CLI

Run the development server on localhost with reload:

fastapi dev

Run the production server:

fastapi run

Add an entrypoint in pyproject.toml

FastAPI CLI will read the entrypoint in pyproject.toml to know where the FastAPI app is declared.

[tool.fastapi]
entrypoint = "my_app.main:app"

Use fastapi with a path

When adding the entrypoint to pyproject.toml is not possible, or the user explicitly asks not to, or it's running an independent small app, you can pass the app file path to the fastapi command:

fastapi dev my_app/main.py

Prefer to set the entrypoint in pyproject.toml when possible.

Use Annotated

Always prefer the Annotated style for parameter and dependency declarations.

It keeps the function signatures working in other contexts, respects the types, allows reusability.

In Parameter Declarations

Use Annotated for parameter declarations, including Path, Query, Header, etc.:

from typing import Annotated

from fastapi import FastAPI, Path, Query

app = FastAPI()


@app.get("/items/{item_id}")
async def read_item(
    item_id: Annotated[int, Path(ge=1, description="The item ID")],
    q: Annotated[str | None, Query(max_length=50)] = None,
):
    return {"message": "Hello World"}

instead of:

# DO NOT DO THIS
@app.get("/items/{item_id}")
async def read_item(
    item_id: int = Path(ge=1, description="The item ID"),
    q: str | None = Query(default=None, max_length=50),
):
    return {"message": "Hello World"}

For Dependencies

Use Annotated for dependencies with Depends().

Unless asked not to, create a new type alias for the dependency to allow re-using it.