starlette-hot-reload 0.3.0

Hot reload for Starlette app with smart asset updates and HTML injection

starlette-hot-reload

Hot reload for Starlette templates and static files

Overview

starlette-hot-reload reloads the browser when your Starlette templates or static assets change. It injects a small client script into HTML responses and uses Server-Sent Events (SSE) to notify the browser about changes.

Demo

Quick Start

Install the package:

uv add starlette-hot-reload
# or
pip install starlette-hot-reload

Enable it in your app lifespan:

from contextlib import asynccontextmanager
from starlette.applications import Starlette
from starlette_hot_reload import hot_reload

@asynccontextmanager
async def lifespan(app: Starlette):
    async with hot_reload(app=app, watch_dirs=["templates", "static"]):
        yield

app = Starlette(
    debug=True,
    lifespan=lifespan,
)

Run your app:

uvicorn main:app

What You Get

• Reloads the browser when watched files change.
• Injects the client script into HTML responses automatically.
• Uses SSE, no websocket.
• Composes with Starlette lifespan context managers.
• Adds no extra runtime dependency beyond Starlette.

Basic Usage

Hot reload only runs when debug=True.

app = Starlette(debug=True)

Watch specific directories:

@asynccontextmanager
async def lifespan(app: Starlette):
    async with hot_reload(
        app=app,
        watch_dirs=["templates", "static", "assets"],
    ):
        yield

Use a custom SSE endpoint:

async with hot_reload(
    app=app,
    watch_dirs=["templates", "static"],
    events_path="/custom-events-path",
):
    ...

Tune filesystem polling:

async with hot_reload(
    app=app,
    watch_dirs=["templates", "static"],
    poll_interval=0.25,
):
    ...

Compose it with other lifespan resources using AsyncExitStack:

from contextlib import AsyncExitStack, asynccontextmanager

@asynccontextmanager
async def lifespan(app: Starlette):
    async with AsyncExitStack() as stack:
        await stack.enter_async_context(
            hot_reload(app=app, watch_dirs=["templates", "static"])
        )
        yield

How It Works

When you request an HTML page, the middleware injects a small client script into the response body. That script opens an SSE connection to the app.

The file watcher polls the directories you configured. When a file changes:

• Watched changes trigger a full page reload.

This package complements server reload tools such as uvicorn --reload. It does not restart your Python process.

Limits

• Hot reload is disabled when debug=False.
• The watcher uses polling, not native OS file notifications.
• Python code changes reload the browser page, but they do not reload server state or restart the app process.
• Script injection targets HTML responses. Non-HTML responses are left alone.

Examples

The repository includes example apps under examples/.

examples/basic

This example shows the smallest Starlette setup with:

• Jinja templates
• Static files
• hot_reload() in the app lifespan

Run it from the repository root:

uv run python -m examples.basic.app

Open http://127.0.0.1:3000 and edit files in examples/basic/templates or examples/basic/static.

examples/with_tailwind

This example shows how to compose starlette-hot-reload with starlette-tailwindcss.

It watches the whole example directory so changes to templates, CSS, and built assets all trigger a browser reload.

Run it from the repository root:

uv run python -m examples.with_tailwind.app

Open http://127.0.0.1:3000 and edit files in examples/with_tailwind/.

Debug Logging

If you want watcher and SSE logs during development, enable Python logging:

import logging
import sys

logging.basicConfig(
    level=logging.DEBUG,
    format="%(asctime)s %(levelname)s [%(name)s] %(message)s",
    datefmt="%Y-%m-%d %H:%M:%S",
    stream=sys.stderr,
)

More Starlette Packages

If you are building server-rendered Starlette apps, these packages fit well with starlette-hot-reload:

• starlette-tailwindcss: Tailwind CSS integration for Starlette apps
• starlette-html-stories: Storybook-like development tools for starlette-html components
• starlette-html: Python-first HTML DSL for server-rendered UI in Starlette

License

MIT