~5 min · Reflex lets you build and deploy full-stack web apps — frontend, backend, and database — in pure Python. No JavaScript, no separate API, no context switching.

We'll build a counter app that lets the user count up or down. In ~20 lines of Python you'll touch the three core pieces of every Reflex app: state, event handlers, and components.

Here is the full code for this example:

import reflex as rx 

class State(rx.State):
    count: int = 0

    @rx.event
    def increment(self):
        self.count += 1

    @rx.event
    def decrement(self):
        self.count -= 1

def index():
    return rx.hstack(
        rx.button(
            "Decrement",
            color_scheme="ruby",
            on_click=State.decrement,
        ),
        rx.heading(State.count, font_size="2em"),
        rx.button(
            "Increment",
            color_scheme="grass",
            on_click=State.increment,
        ),
        spacing="4",
    )

app = rx.App()
app.add_page(index)

Let's break this example down.

Import Reflex as rx. All Reflex objects are accessed as rx.*.

State holds the app's mutable data. Variables declared here are called vars. Our counter has one: count, starting at 0.

Event handlers are the only way to modify state. They're triggered by user actions (clicks, typing, etc.) — those actions are called events. Our counter has two handlers: increment and decrement.

The UI is built from components (rx.hstack, rx.button, rx.heading) that can be nested and styled with CSS or Tailwind. Reflex ships with 50+ built-in components, and you can wrap any React component.

Components reference state vars (rx.heading(State.count, …)) and reactively re-render when state changes. Event triggers (on_click=State.decrement) wire UI to handlers.

The sequence goes like this:

1. User clicks "Increment".
2. on_click fires.
3. State.increment runs on the server.
4. State.count is updated.
5. UI re-renders with the new value.

Create the app and register the page at the base route.

🎉 You've built a fully interactive web app in pure Python.

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