Flask

Flask gives you routing, templates, and a request context — nothing more. Everything else (ORM, auth, migrations) comes from the large ecosystem of Flask extensions. Its simplicity makes it the go-to for small APIs, microservices, internal tools, and projects where Django’s batteries are overhead. Flask has no required project layout, so it’s quick to prototype and easy to structure exactly as your project demands.

Quick start

pip install flask

# app.py
from flask import Flask, jsonify, request, abort

app = Flask(__name__)

posts = [
    {"id": 1, "title": "Hello Flask", "body": "Getting started."},
]

@app.get("/posts")
def list_posts():
    return jsonify(posts)

@app.get("/posts/<int:post_id>")
def get_post(post_id):
    post = next((p for p in posts if p["id"] == post_id), None)
    if post is None:
        abort(404)
    return jsonify(post)

@app.post("/posts")
def create_post():
    data = request.get_json()
    new_post = {"id": len(posts) + 1, **data}
    posts.append(new_post)
    return jsonify(new_post), 201

if __name__ == "__main__":
    app.run(debug=True)

flask run --debug
# Visit http://127.0.0.1:5000/posts

When to use

Flask is the best choice for small-to-medium Python APIs, internal tools, and projects where you want to pick your own ORM and auth strategy. Its lack of opinions is a feature — not a limitation — when the project’s needs are clearly defined. For larger applications with complex data models, Django’s batteries save significant time. For high-throughput async APIs, FastAPI offers better performance and automatic docs.