reflex-dev/reflex

Reflex is a library for building full-stack web apps using only Python. Normally a web app has a frontend in JavaScript and a backend in a language like Python, and the two halves have to talk to each other. Reflex lets you write both halves in Python in a single file, so you do not have to learn JavaScript to ship a working app. You write the page as a Python function that returns components: a heading, an input box, a button, and layout containers such as a centered column. The README says Reflex comes with more than 60 built-in components, and you can also wrap your own. Components are styled with keyword arguments that map to CSS, and can be nested to build complex layouts. The dynamic parts of the app live in a State class. State variables represent the data the page depends on, and event handlers are methods on the state that update those variables in response to user actions like clicking a button or typing in a field. The UI is a function of the state, so when the state changes the page updates. Using yield inside a handler streams an interim update to the UI, otherwise the update happens when the handler finishes. The README walks through a small example that calls an image generation API and shows the returned image once ready. To get started you create a project directory, install the uv project manager, add Reflex (which requires Python 3.10 or newer), run an init command to scaffold a template, then run the dev server on localhost. There is also a hosted AI-powered app builder called Reflex Build that generates Reflex apps, and your app can be deployed with a single command or self-hosted.