There is some more spot a request can carry data: cookies. That is where things like a auth session token usually ride along. 🍪The nice part: reading a cookie looks exactly like reading a query or path value. Same pattern just a new helper.

Reading a cookie

Import Cookie from fastapi and use it inside Annotated, just like Query and Path.

from typing import Annotated, Optionalfrom fastapi import Cookie, FastAPIapp = FastAPI()@app.get("/blog")async def read_blog(session_id: Annotated[Optional[str], Cookie()] = None):    return {"session_id": session_id}

Let's understand the code:

1. Cookie() tells FastAPI to look for session_id in the request cookies, not the query string.

2. The type is Optional[str] with a default of None, so the cookie is optional. No cookie, no problem.

3. Cookie takes the same extras as Query and Path, like min_length or a description, since they are all siblings.

Send a request with a cookie session_id=abc123 and you get back {"session_id": "abc123"}.

Next: Header Parameters. Cookies have a close cousin, the request header, where things like User-Agent and auth tokens live. Reading headers uses the very same pattern, with one small naming quirk we will sort out. Okie dokie, bye.