Reflex - Build Full-Stack Python Apps Without JavaScript

Reflex is an open-source, full-stack Python app platform built by Pynecone, Inc., a Y Combinator-backed company. It gives developers a single library to build both the frontend and backend of production-grade web apps without writing JavaScript. Under the hood, Reflex compiles your Python source code into a React/Next.js frontend and a FastAPI backend, with WebSockets handling communication between the two. It powers over 1 million applications and has earned more than 28,000 stars on GitHub.

Features:

• Build apps in pure Python (no JavaScript required)
• AI Builder (describe your idea, Reflex generates and tests it)
• Agent Toolkit (connect MCP and Skills to your coding assistant)
• 60+ built-in, customizable UI components
• Manage state via a Python class (class State)
• Single command deploy to AWS, GCP, Azure, or on-prem
• Apache 2.0 open source (full control, no vendor lock-in)
• WebSocket-based communication between app's frontend and backend
• Supports AI agents and async event handlers

FAQs about Reflex:

What is Reflex?

Reflex is an open-source platform that lets you build and deploy full-stack web apps entirely in Python. You just write the UI and logic in the same language, and it compiles everything into a React frontend and a FastAPI backend. It's one of the fastest-growing tools in one of the most popular programming languages, and it’s trusted by 30% of Fortune 500 companies to build internal tools at scale.

How does Reflex help me build web apps in pure Python?

With Reflex, your app's UI is built using Python functions that map directly to React components. State lives inside a Python class, and any method that changes a variable automatically updates the UI.

That said, the frontend and backend communicate through WebSockets, so the experience feels real-time without extra setup. You can let Reflex run locally, and your app is live at http://localhost:3000.

What's a good example app I can reference to get started with Reflex?

A great example is the AI image generation app in Reflex's official docs. This shows how to define a UI, manage state, and call an external model, all in Python.

There's also a sales management app, a data dashboard with charts and tables, and an NBA stats visualizer in their template library. Each one comes with full source code you can copy and run. They're short enough to follow in an afternoon.

How do I create my first app with Reflex?

Getting your first Reflex app running takes just a few minutes. Here's how:

1. Before anything else, set up a virtual environment. Reflex's docs strongly recommend it to avoid PATH issues with the reflex command.
2. Then install Reflex by running pip install reflex inside your virtual environment. uv add reflex works if you're using uv.
3. Make a new directory for your app and navigate into it by running mkdir my_app && cd my_app.
4. Run reflex init to initialize setup. This scaffolds your project structure and generates the starter files.
5. Run reflex run to start the development server. Your app will be live at http://localhost:3000 within seconds.
6. Open my_app_name/my_app_name.py and start editing. Reflex picks up every change instantly, keeping you from refreshing manually.

Do beginners require CSS and HTML background to build full-stack Reflex apps?

No, not really. If you already know Python, then you have most of what you need. Reflex handles frontend compilation, so you don’t have to write HTML tags or CSS files manually.

You can style components by passing CSS properties as keyword arguments in Python, but that’s optional. That said, a light familiarity with how web layouts work will make things click faster, especially for more complex apps.

Can Reflex generate customizable web apps?

Yes, Reflex gives you full control over how your app looks and behaves. You can style any component with standard CSS properties, build custom components from scratch, or pull in third-party Python libraries from PyPI.

The AI Builder can generate a starting point from a simple prompt description, and you can then edit the source code however you like. There's no walled garden, as everything compiles down to standard React and FastAPI.

Is Reflex for free?

Yes, the core Reflex framework is free and open source under the Apache 2.0 license. In the free tier, you get 150 AI Builder credits per month, one hosted app on shared compute, AI-assisted testing, the local Agent Toolkit with MCP and Skills, and unlimited collaborators.

Community support is also available through Discord and GitHub. It's a solid starting point for solo developers or small teams building their first app.

It also has an Enterprise plan that’s designed for teams. Here’s what you get:

• Enterprise (contact sales)

The Enterprise tier offers unlimited AI Builder credits, unlimited apps on dedicated compute, and one-click deploy to AWS, GCP, Azure, Databricks, or on-prem. It also adds SSO/SAML, RBAC, HIPAA BAA, private project support, 90-day log retention, and a forward-deployed engineer for onboarding. Pricing is custom, so you'll need to book a demo with their sales team.

Which is better for building full-stack web apps: Reflex, Retool, or Appsmith?

It depends on what your team needs and how much control you want over your codebase. Here's how each tool stacks up:

1. Reflex

Reflex is a code-first, full-stack Python framework; you write real Python for both the frontend and backend, with no JavaScript required. It's built for developers who want production-grade output, full control over their source code, and the flexibility to build anything from internal tools to customer-facing apps. Teams already working in Python will feel right at home, since there's no new language to learn.

2. Retool

Retool is a low-code drag-and-drop builder designed for spinning up internal dashboards and admin panels fast. It connects to databases and APIs out of the box, which makes it genuinely quick for straightforward data tools.

Where it falls short against Reflex is when you need custom logic, a unique UI, or code you actually own. Retool's flexibility has its limits, and you're also tied to their platform.

3. Appsmith

Appsmith is an open-source, low-code alternative to Retool with a similar drag-and-drop interface. It's a reasonable pick for teams that want a self-hostable no-code builder without the Retool price tag.

Compared to Reflex, Appsmith is faster to start but runs into the same limitations. Complex apps with custom behavior quickly outgrow what a GUI builder can handle.

Bottom line:

• Choose Retool or Appsmith if you need a dashboard or internal tool running fast with minimal coding.
• Choose Reflex if you're a Python developer who wants full control, custom logic, and a production-ready codebase you own.