Flet — Build Multiplatform Apps in Python Without Frontend Experience

Introduction

Flet is a framework that enables Python developers to build interactive multiplatform user interfaces without learning frontend technologies. It provides Python bindings for Flutter widgets, allowing you to create web, desktop (Windows, macOS, Linux), and mobile apps using pure Python with real-time UI updates.

What Flet Does

• Wraps Flutter's widget library with Pythonic APIs for building rich UIs
• Deploys to web, Windows, macOS, Linux, iOS, and Android from one codebase
• Provides real-time UI updates via WebSocket communication between Python backend and Flutter frontend
• Includes 100+ pre-built controls (data tables, charts, navigation, forms, animations)
• Supports both single-user desktop mode and multi-user web app deployment

Architecture Overview

Flet operates as a client-server architecture where the Python program acts as the server managing application state and logic, while a Flutter-based client renders the UI. Communication happens over WebSockets, allowing real-time bidirectional updates. In desktop mode, the Flutter client runs as a native window alongside the Python process. In web mode, the Flutter client compiles to JavaScript and runs in the browser while the Python backend serves requests. This separation means the UI rendering benefits from Flutter's performance while application logic stays in pure Python.

Self-Hosting & Configuration

• Install with pip install flet and create apps as standard Python scripts
• Run desktop apps directly with python main.py (opens a native window)
• Serve as web apps with flet run --web for development or flet publish for static hosting
• Package desktop apps into standalone executables with flet pack
• Deploy web apps to Flet Cloud, self-hosted servers, or any platform supporting Python

Key Features

• Pure Python development with no HTML, CSS, or JavaScript required
• Real-time reactive UI updates without manual DOM manipulation
• Cross-platform output from a single codebase (web, desktop, mobile)
• Hot reload during development for instant feedback
• Accessibility support inherited from Flutter's widget system

Comparison with Similar Tools

• Streamlit — focused on data dashboards with a simpler model; Flet provides a general-purpose app framework with richer UI controls
• Gradio — designed for ML model demos; Flet is a full application framework not limited to data science
• NiceGUI — Python web UI framework; Flet additionally targets native desktop and mobile platforms via Flutter
• Tkinter — desktop-only with dated appearance; Flet offers modern Material Design widgets across all platforms
• PyQt/PySide — powerful but complex desktop toolkit; Flet provides simpler APIs with web and mobile deployment included

FAQ

Q: Does Flet require Flutter to be installed? A: No. Flet bundles the Flutter runtime. You only need Python installed to build and run Flet apps.

Q: Can Flet apps work offline? A: Desktop and mobile apps work fully offline. Web apps require a connection to the Python backend unless published as static Progressive Web Apps.

Q: How does performance compare to native Flutter apps? A: UI rendering performance is equivalent since Flet uses Flutter's engine. The WebSocket communication adds minimal latency (typically under 10ms locally) for state updates.

Q: Can I use existing Python libraries in Flet apps? A: Yes. Since app logic runs in standard Python, you can use any Python package (NumPy, pandas, requests, SQLAlchemy, etc.) alongside Flet UI code.

Sources

• https://github.com/flet-dev/flet
• https://flet.dev/docs