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build Python WSGI applications with routing, request handling, and Jinja templates

OSS scale score 348.5OSS health 82Update pace 1 commits/30d
About these scores

OSS scale score is an unbounded metric that log-compresses and weights Stars, Watchers, Forks, and Contributors. Discovery score is the current OSS scale score minus the score at discovery. Update pace is commits in the last 30 days, growth momentum is the OSS scale score difference within the recent observation window, and OSS health is a 0–100 rating based on available recency, Community Health, and release data.

Stars
74,801
Primary language
Python
License
BSD-3-Clause
Repository last updated
Sep 8, 2026
On this page

Overview

Flask is a lightweight WSGI web application framework for Python. Built on Werkzeug and Jinja, it provides routing, requests and responses, templates, sessions, and related web primitives while leaving project layout and additional libraries to the application.

Features and best fit

Based on official documentation; not hands-on tested · Content checked:

Key features

Map URLs to Python functions with route decorators

Create a Flask application and bind URLs to view functions with @app.route() or method-specific decorators, while using framework APIs for request data, responses, redirects, and URL generation.

Sources: [2][3]

Combine built-in Jinja templates with extensions chosen by the application

Jinja is integrated for template rendering, while Flask deliberately avoids enforcing a project layout or database stack. Additional capabilities can come from community extensions and other libraries.

Sources: [2][3]

Best fit

Fits Python web and API projects that want a small core and explicit composition

It works well for applications that need to start small, choose their own supporting libraries, and grow into more complex web services without a large prescribed architecture.

Sources: [2]

Before adoption

Do not use the built-in development server in production

The official quickstart and deployment documentation say the flask run development server and debugger are for local development only. Production deployments should use a dedicated WSGI server or hosting platform.

Sources: [3][4]

Flask 3.1.3 requires Python 3.9+ and includes a security fix

The 3.1.3 package metadata requires Python 3.9 or newer. The 3.1.3 release is a security fix release addressing session accessed-state behavior for key-only operations.

Sources: [5][6]

Official sources

  1. [1]pallets/flask repository(2026-09-30)
  2. [2]Flask README(2026-09-30)
  3. [3]Flask 3.1.3 quickstart(2026-09-30)
  4. [4]Flask production deployment guide(2026-09-30)
  5. [5]Flask 3.1.3 package metadata(2026-09-30)
  6. [6]Flask 3.1.3 release(2026-09-30)
  7. [7]Flask BSD-3-Clause license(2026-09-30)
Supplemental curator note

Flask keeps the core small and lets applications choose supporting libraries, but production servers, databases, authentication, and other infrastructure remain explicit design choices. Version 3.1.3 is a security fix release.

Try it in 3 steps

  1. 1

    Install Flask 3.1.3

    Flask 3.1.3 requires Python 3.9 or newer. Install it in a virtual environment with the version pinned.

    python -m pip install Flask==3.1.3
  2. 2

    Create a minimal application

    Save the Flask application and root route in app.py.

    from flask import Flask app = Flask(__name__) @app.route("/") def hello(): return "Hello, World!"
  3. 3

    Run the development server

    Open http://127.0.0.1:5000/ to verify the route. The built-in server is for local development only; use a production WSGI server or hosting platform for deployment.

    flask --app app run
Check the official README

Growth

Growth trends · Last 30 days

74,801 Stars

Trend data is still being collected.

Development activity

Last 90 days · weekly

Commits (last 30 days)
1
Open PRs
3

Development activity is still being collected.

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GitHub data

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GitHub Topics

  • python
  • flask
  • wsgi
  • web-framework
  • werkzeug
  • jinja
  • pallets
Stars
74,801
Forks
17,010
Watchers
2,118
Open issues
1
Contributors
400
Owner type
Organization
Primary language
Python
Repository last updated
Sep 8, 2026
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