Flask

A simple framework for building complex web applications.

flask Permissive license BSD-3-Clause Active ★ 72,192 v3.1.3 released 2026-02-19

Install

flask on PyPI

pip

pip install flask

uv

uv add flask

poetry

poetry add flask

Package facts

License	BSD-3-Clause (permissive)
Python support	supports the current Python release (>=3.9)
Install friction	low — pure-Python wheel
Runtime dependencies	7 — blinker, click, importlib-metadata, itsdangerous, jinja2, markupsafe, werkzeug
Maintenance	actively maintained — 175 days since the last release
Last repo commit	2026-08-11
First released	2010-04-16
Popularity	one of the top 1,000 most-downloaded packages on PyPI (30-day window, as of 2026-08-13)
Known vulnerabilities	none known (OSV.dev, checked 2026-08-13)

Evidence: flask-3.1.3-py3-none-any.whl

Development Status :: 5 - Production/StableEnvironment :: Web EnvironmentFramework :: FlaskIntended Audience :: DevelopersOperating System :: OS IndependentProgramming Language :: PythonTopic :: Internet :: WWW/HTTP :: Dynamic ContentTopic :: Internet :: WWW/HTTP :: WSGITopic :: Internet :: WWW/HTTP :: WSGI :: ApplicationTopic :: Software Development :: Libraries :: Application FrameworksTyping :: Typed

About Flask

from the package's own PyPI description — quoted content, verbatim

Flask

Flask is a lightweight WSGI web application framework. It is designed to make getting started quick and easy, with the ability to scale up to complex applications. It began as a simple wrapper around Werkzeug and Jinja, and has become one of the most popular Python web application frameworks.

Flask offers suggestions, but doesn't enforce any dependencies or project layout. It is up to the developer to choose the tools and libraries they want to use. There are many extensions provided by the community that make adding new functionality easy.

A Simple Example

# save this as app.py
from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello, World!"

$ flask run
  * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Donate

The Pallets organization develops and supports Flask and the libraries it uses. In order to...

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AI interpretation — verify before relying

AI-generated interpretation of the package facts above; every digit, version, license, or vulnerability id it cites is grounded in the facts already shown on this page

Flask is a lightweight WSGI web framework for building web applications from simple to complex, with minimal enforcement of structure or dependencies.

Low install friction with seven well-established runtime dependencies; actively maintained with recent commits indicating strong community support and stability.

BSD-3-Clause permissive license allows commercial and private use with minimal restrictions, requiring only retention of copyright and license notices.

Usage

pip install flask

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run()

Requires Python 3.9 or later; werkzeug and jinja2 must be available at runtime.

Verdict: Flask is a production-stable, actively maintained web framework with no known vulnerabilities, low install friction, and permissive licensing. Its minimal dependencies and broad adoption make it a reliable choice for web application development.

Needs verification

Whether the 175-day release cadence reflects planned maintenance cycles or slower update frequency.
Performance characteristics and scalability limits for high-traffic production deployments.

lightweight web framework pythonwsgi application frameworkpython web developmentmicroframework routingsimple web application builderpython rest api frameworkweb application framework