Live Reloading

When building your app it can be useful to view your changes in a web browser as you make them. FastHTML supports live reloading which means that it watches for any changes to your code and automatically refreshes the webpage in your browser.

To enable live reloading simply replace FastHTML in your app with FastHTMLWithLiveReload.

from fasthtml.common import *
app = FastHTMLWithLiveReload()

Then in your terminal run uvicorn with reloading enabled.

uvicorn main:app --reload

⚠️ Gotchas - A reload is only triggered when you save your changes. - FastHTMLWithLiveReload should only be used during development. - If your app spans multiple directories you might need to use the --reload-dir flag to watch all files in each directory. See the uvicorn docs for more info.

Live reloading with fast_app

In development the fast_app function provides the same functionality. It instantiates the FastHTMLWithLiveReload class if you pass live=True:

main.py

from fasthtml.common import *

1app, rt = fast_app(live=True)

2serve()

1

fast_app() instantiates the FastHTMLWithLiveReload class.

2

serve() is a wrapper around a uvicorn call.

To run main.py in live reload mode, just do python main.py. We recommend turning off live reload when deploying your app to production.