FastAPI vs Flask vs Django comparison

Introduction

These are popular tools to build web apps and APIs. Knowing their differences helps you pick the right one for your project.

You want a simple and lightweight web app or API quickly.

You need automatic data validation and documentation for your API.

You want a full-featured web framework with built-in admin and database tools.

You are building a small project or prototype fast.

You want to handle complex projects with many features and users.

Syntax

FastAPI

FastAPI: from fastapi import FastAPI
app = FastAPI()

Flask: from flask import Flask
app = Flask(__name__)

Django: # Uses project and app structure, not a single code snippet

FastAPI and Flask use simple Python code to create apps.

Django uses a structured project with settings, apps, and models.

Examples

FastAPI example with async function and automatic docs.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get('/')
async def read_root():
    return {"message": "Hello from FastAPI"}

Flask example with simple route and function.

FastAPI

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello():
    return "Hello from Flask"

Django example with view function and URL routing.

FastAPI

# Django uses views.py and urls.py files
# views.py
from django.http import HttpResponse

def home(request):
    return HttpResponse("Hello from Django")

# urls.py
from django.urls import path
from . import views

urlpatterns = [
    path('', views.home),
]

Sample Program

This FastAPI app responds with a JSON message at the root URL. It uses async function and returns a dictionary that FastAPI converts to JSON automatically.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get('/')
async def read_root():
    return {"message": "Hello from FastAPI"}

Important Notes

FastAPI is great for APIs with automatic validation and docs.

Flask is simple and flexible but needs more setup for big projects.

Django is powerful with many built-in features but has more learning curve.

Summary

FastAPI is modern, fast, and good for APIs with type checking.

Flask is minimal and easy to start with for small apps.

Django is full-featured and suits large, complex web apps.