Environment Variables & Configuration - Backend Development with FastAPI

1. Environment Variables (.env)

An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. In backend development, we use them to store:

API Keys and secrets
Database connection strings (URLs)
Application ports and modes (e.g., debug vs. production)

The `.env` File

Instead of hardcoding configurations in our code, we save them in a local text file named .env:

# .env
DATABASE_URL=postgresql://user:pass@localhost:5432/mydb
SECRET_KEY=supersecretjwttokenkey
DEBUG=True
PORT=8000

[!CAUTION] Never commit your .env file to Git! It contains sensitive credentials. Always add .env to your .gitignore file. Instead, commit a .env.example file that lists the keys but leaves the values blank.

2. Managing Settings with Pydantic Settings

While you can access environment variables using Python’s built-in os.environ.get(), it does not validate data types or check if required fields are missing. The industry-standard way to manage configuration in FastAPI is using pydantic-settings.

Installation

pip install pydantic-settings
# or with uv
uv pip install pydantic-settings

Creating a Settings Config

Inherit from pydantic_settings.BaseSettings. Pydantic will automatically load fields from environment variables (case-insensitive) and validate their types.

# app/config.py
from pydantic_settings import BaseSettings, SettingsConfigDict

class Settings(BaseSettings):
    # Automatically loaded from env or defaults to local
    DATABASE_URL: str = "sqlite:///./local.db"
    SECRET_KEY: str
    DEBUG: bool = False
    PORT: int = 8000

    # Configures settings behaviour to load from a .env file
    model_config = SettingsConfigDict(env_file=".env", extra="ignore")

# Instantiate settings
settings = Settings()

Accessing Settings in Your App

Now, import settings anywhere in your application:

# app/main.py
from fastapi import FastAPI
from app.config import settings

app = FastAPI(debug=settings.DEBUG)

@app.get("/")
def read_root():
    return {"status": "ok", "db": settings.DATABASE_URL}

​1. Environment Variables (.env)

​The .env File

​2. Managing Settings with Pydantic Settings

​Installation

​Creating a Settings Config

​Accessing Settings in Your App