Is it possible to check for Production or Development mode?

[retifrav]

Description

The fastapi run starts FastAPI in Production mode, and fastapi dev starts FastAPI in Development mode. But is it possible to detect/check which mode is it running in now? I'd expect something like:

api = FastAPI()

if api.DevelopmentMode:
    print("Running in Development mode")
else:
    print("Running in Production mode")

I couldn't find anything related in the FastAPI class reference.

Operating System

macOS

FastAPI Version

0.111.0

Pydantic Version

2.7.3

Python Version

3.12.3

[YuriiMotov]

FastAPI CLI doesn't pass this information to FastAPI app.

The only difference between these commands is that FastAPI CLI uses different defaults for parameters to run ASGI server (host address and reload).

And since it's only default parameters, they can be overridden. For example command fastapi run main.py --host 127.0.0.1 --reload is a full equivalent of fastapi dev main.py.

As I know the common way to determine whether the app is running in prod or dev environment is to use ENV variable.
Just set ENV variable with the name like RUN_MODE to DEV on your local machine and to PROD on your production server

export RUN_MODE="DEV"

Then read this variable in your app:

from fastapi import FastAPI
import os

app = FastAPI()

@app.get("/")
def index():
    return os.environ.get('RUN_MODE', 'NONE')

[retifrav]

Yes, that's exactly how I did it for now - with an environment variable. Just wanted to check for "in-code" options, in case I missed something from the documentation. Thank you for the explanation!

[Grz3hu]

You can simply check check what command has been used using system library

from fastapi import FastAPI, Query

app = FastAPI()

import sys
print(str(sys.argv))

output:
['/home/grz3hu/Documents/Projects/Python/FastAPI/MySample/env/bin/fastapi', 'run']