Flask

Open Source

The Python micro framework for building web applications.

Backend Frameworks

Python Backend Frameworks

Published 29 May 2026 · Last updated 27 September 2026

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Scores

Popularity3/5

One of the most downloaded Python packages; widely used for simple APIs and prototyping.

Learning Curve2/5

Micro-framework that gets out of your way; a simple API is fewer than 20 lines.

Flexibility4/5

Micro-framework with no opinions; every component is replaceable.

Performance4/5

Lightweight core with low overhead; performance is bounded by Python's runtime speed.

Portability4/5

Minimal standard Python HTTP patterns; straightforward to migrate to FastAPI or Starlette.

About Flask

Flask is a lightweight WSGI web framework for Python, first released in 2010 and maintained by the Pallets project. It is deliberately a micro-framework: the core provides routing, a development server with an interactive debugger, request and response handling, Jinja2 templating, and signed session cookies, and nothing else by default. Developers choose the database, ORM, authentication library, and form validation from Flask's ecosystem of extensions.

Routing uses Python decorators to map URL patterns to view functions. Blueprints split a larger application into modular components that register independently, and the Jinja2 templating engine supports inheritance, macros, and filters. Since Flask 2.0, views can be written as async def; under WSGI each async view runs in its own event loop per request, so apps that are async throughout usually choose Quart, the ASGI re-implementation of Flask's API, or FastAPI instead.

Popular extensions include Flask-SQLAlchemy for the ORM, Flask-Migrate for Alembic migrations, Flask-Login for sessions, Flask-WTF for forms, and Flask-CORS. Flask apps run on WSGI servers such as Gunicorn or uWSGI behind Nginx, or in Docker containers on any cloud platform. The small core makes Flask a common first framework and a good fit for small APIs, prototypes, and services where the team wants to pick every component itself.

Key Features

Minimal core: routing, request handling, and signed sessions
Built-in development server and interactive debugger
Jinja2 templating for server-side rendering
Decorator-based URL routing
Blueprints for organising larger applications into modules
Async views (async def) supported since Flask 2.0
Large ecosystem of extensions for databases, auth, forms, and CORS

Pros

A working app takes a few lines of code
Free choice of database, ORM, and authentication method
Gentle learning curve, good for beginners, prototypes, and small services
Mature, stable, and very widely used, with extensive examples
Extensions cover most common needs

Cons

Architecture and project structure are left to the team, which can lead to inconsistency
Database, auth, and admin have to be assembled from extensions
Async views run per request under WSGI; fully async apps are better served by Quart or FastAPI
Fewer security features built in than Django
Large applications need deliberate structure to stay maintainable

Flask Pricing

Open Source

Tech Stacks with Flask

MLOps Pipeline

Project

Production-grade ML infrastructure. PyTorch for model training, Apache Airflow (or Dagster or Prefect) for orchestration, dbt for feature transformations, and Snowflake as the data warehouse, with Docker as an optional containerization addition.

Flask

Backend

Python

Programming

Snowflake

Databases

Google Cloud Platform

Hosting

Data

Data

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HTMX + Flask

Project

The simplest way to add dynamic interactions to a Flask app. HTMX attributes in Jinja2 templates, server returns HTML fragments. Perfect for beginners building server-rendered web apps with Python.

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Backend

Programming

Databases

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Flask + HTML Templates

Project

Minimal Flask app serving Jinja2 HTML templates, great for small projects and prototypes.

Backend

Programming

Databases

Hosting

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Learning Resources

View all →

When to Pair Supabase with a Backend Framework

Supabase is pitched as a backend replacement — but for lightweight frameworks like Flask or FastAPI, it works just as well as a managed data layer. Here's why the combination makes sense.

article· 5m

Tools Related to Flask

Child tools of Flask(1)

Flask-Login

Session management for Flask: tracks the logged-in user across requests, handles remember-me cookies, and protects views — without dictating how you store users or passwords.

Open Source

Authentication

5/5

Flask-Login is a third-party session-management extension for Flask, which ships with no auth system of its own.

Works well with Flask(2)

HTMX

HTMX gives HTML superpowers by letting you access AJAX, CSS Transitions, WebSockets, and Server-Sent Events directly through HTML attributes — no JavaScript required. It works with any backend language.

Open Source

Frontend Frameworks

4/5

Flask serves HTMX-compatible HTML fragments via Jinja2 templates — Flask's request/response cycle maps cleanly to HTMX's partial HTML swap model.

PyTorch

PyTorch is the leading open-source deep learning framework, providing dynamic computation graphs, GPU-accelerated tensor operations, and a rich ecosystem for building and deploying neural networks.

Open Source

Data & ML Libraries

3/5

Flask is a simpler, synchronous alternative to FastAPI for serving a trained PyTorch model behind a REST endpoint.

Built on (1)

Python

Python is a high-level, interpreted, dynamically typed programming language emphasising readability and simplicity. It dominates data science, machine learning, and general-purpose scripting.

Open Source

Programming Languages

5/5

Flask is a lightweight Python web framework with minimal core.

Alternatives to Flask(10)

FastAPI

FastAPI is a modern Python framework for building APIs from standard type hints, with automatic OpenAPI documentation, Pydantic validation, and native async support.

Freemium

Backend Frameworks

4/5

FastAPI is async-first and auto-generates OpenAPI docs via type hints; Flask is sync-first, more minimal, and requires more manual wiring.

Django

High-level Python web framework for rapid development with clean, pragmatic design. Includes built-in ORM, admin panel, authentication, and security features.

Open Source

Backend Frameworks

4/5

Both Python web frameworks; Django bundles ORM, auth, and admin out of the box, Flask gives a minimal foundation with more flexibility.

Spring Boot

Spring Boot is an opinionated Java framework that simplifies the creation of production-ready Spring applications with minimal configuration and embedded servers.

Open Source

Backend Frameworks

3/5

Flask is a minimal Python framework; Spring Boot is a Java enterprise framework — different language ecosystems.

Axum

Axum is an ergonomic, macro-free web framework for Rust built on top of Tokio, Hyper, and Tower. It offers type-safe request extractors, composable middleware via Tower, and minimal boilerplate for building async HTTP APIs.

Open Source

Backend Frameworks

3/5

Axum is a lightweight Rust framework; Flask is a minimal Python framework — different language ecosystems.