fastui

What it is and what it does

FastUI is a Python framework for building web application interfaces by defining UI components declaratively using Pydantic models. Instead of writing React or JavaScript, you describe your UI in Python on the backend, and FastUI serializes those descriptions to the frontend where a pre-built React application renders them. The core idea is that the backend fully controls the UI structure and behavior—the frontend is essentially a dumb renderer that knows how to display FastUI components.

You define routes that return lists of FastUI components (like Page, Table, Heading, Link), and the frontend fetches and renders them. This approach eliminates the need to write JavaScript or manage npm dependencies if you use the prebuilt version, and it keeps all application logic in Python. The package itself provides Pydantic models for UI components and utilities; it works with FastAPI but does not depend on it, so it can integrate with other Python web frameworks.

Use it for:

• Build internal admin dashboards or data-viewing tools in Python without touching JavaScript or npm.
• Create responsive web applications where the backend controls all UI structure and navigation flow.
• Prototype web UIs quickly using Python and Pydantic validation without frontend development overhead.
• Share UI component definitions between backend and frontend via JSON Schema and Pydantic validation.
• Develop applications where frontend and backend deployment cycles can be completely decoupled.

Worth the install?

AI-flagged interpretation of the facts on this page — verify before relying

FastUI lets you build responsive web application UIs by writing declarative Python code with Pydantic models, which are rendered as React components on the frontend without writing JavaScript.

No. The project is abandoned—the repository is archived, no commits since April 2026, and the description explicitly notes inactivity. While the code is permissively licensed and has low install friction, adopting an unmaintained framework for new projects carries significant risk: npm dependencies will drift, React ecosystem changes will break rendering, and bugs will go unfixed. Existing applications may continue to work short-term, but long-term viability is not assured.

Install

fastui on PyPI

pip install fastui

uv add fastui

poetry add fastui

Installing fastui

Before you install

Installation is straightforward with low friction—a pure Python wheel depending only on pydantic. However, the project is now abandoned as of the latest release; the repository is archived and no active maintenance is occurring.

License in practice

MIT license is permissive, allowing commercial and private use with minimal restrictions, making it safe to adopt from a licensing perspective.

Quickstart

pip install fastui

from fastui import FastUI, components as c
from pydantic import BaseModel

class User(BaseModel):
    name: str

def get_ui() -> list:
    return [c.Page(components=[c.Heading(text='Hello', level=2)])]

Requires Python 3.10 or later. Rendering requires the frontend npm packages (@pydantic/fastui-prebuilt or custom React setup) to be deployed separately.

Verify before relying

• Whether the prebuilt CDN version (@pydantic/fastui-prebuilt) remains available and functional after project abandonment
• Current state of the npm packages (@pydantic/fastui, @pydantic/fastui-bootstrap) and whether they receive any maintenance
• Whether existing FastUI applications will continue to work as browser and React ecosystem dependencies evolve

Package facts

Evidence: fastui-0.9.0-py3-none-any.whl

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