Response Status Code

The same way you can specify a response model, you can also declare the HTTP status code used for the response with the parameter status_code in any of the path operations:

  • @app.get()
  • @app.post()
  • @app.put()
  • @app.delete()
  • etc.
from fastapi import FastAPI

app = FastAPI()


@app.post("/items/", status_code=201)
async def create_item(name: str):
    return {"name": name}

Note

Notice that status_code is a parameter of the "decorator" method (get, post, etc). Not of your path operation function, like all the parameters and body.

The status_code parameter receives a number with the HTTP status code.

It will:

  • Return that status code in the response.
  • Document it as such in the OpenAPI schema (and so, in the user interfaces):

Note

Some response codes (see the next section) indicate that the response does not have a body.

FastAPI knows this, and will produce OpenAPI docs that state there is no response body.

About HTTP status codes

Note

If you already know what HTTP status codes are, skip to the next section.

In HTTP, you send a numeric status code of 3 digits as part of the response.

These status codes have a name associated to recognize them, but the important part is the number.

In short:

  • 100 and above are for "Information". You rarely use them directly. Responses with these status codes cannot have a body.
  • 200 and above are for "Successful" responses. These are the ones you would use the most.
    • 200 is the default status code, which means everything was "OK".
    • Another example would be 201, "Created". It is commonly used after creating a new record in the database.
    • A special case is 204, "No Content". This response is used when there is no content to return to the client, and so the response must not have a body.
  • 300 and above are for "Redirection". Responses with these status codes may or may not have a body, except for 304, "Not Modified", which must not have one.
  • 400 and above are for "Client error" responses. These are the second type you would probably use the most.
    • An example is 404, for a "Not Found" response.
    • For generic errors from the client, you can just use 400.
  • 500 and above are for server errors. You almost never use them directly. When something goes wrong at some part in your application code, or server, it will automatically return one of these status codes.

Tip

To know more about each status code and which code is for what, check the MDN documentation about HTTP status codes.

Shortcut to remember the names

Let's see the previous example again:

from fastapi import FastAPI

app = FastAPI()


@app.post("/items/", status_code=201)
async def create_item(name: str):
    return {"name": name}

201 is the status code for "Created".

But you don't have to memorize what each of these codes mean.

You can use the convenience variables from starlette.status.

from fastapi import FastAPI
from starlette.status import HTTP_201_CREATED

app = FastAPI()


@app.post("/items/", status_code=HTTP_201_CREATED)
async def create_item(name: str):
    return {"name": name}

They are just a convenience, they hold the same number, but that way you can use the editor's autocomplete to find them:

Changing the default

Later, in a more advanced part of the tutorial/user guide, you will see how to return a different status code than the default you are declaring here.