FastHTML

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FastHTML

Welcome to the official FastHTML documentation.

FastHTML is a new next-generation web framework for fast, scalable web
applications with minimal, compact code. It’s designed to be:

• Powerful and expressive enough to build the most advanced, interactive
  web apps you can imagine.
• Fast and lightweight, so you can write less code and get more done.
• Easy to learn and use, with a simple, intuitive syntax that makes it
  easy to build complex apps quickly.

FastHTML apps are just Python code, so you can use FastHTML with the
full power of the Python language and ecosystem. FastHTML’s
functionality maps 1:1 directly to HTML and HTTP, but allows them to be
encapsulated using good software engineering practices—so you’ll need to
understand these foundations to use this library fully. To understand
how and why this works, please read this first:
about.fastht.ml.

Installation

Since fasthtml is a Python library, you can install it with:

pip install python-fasthtml

In the near future, we hope to add component libraries that can likewise
be installed via pip.

Usage

For a minimal app, create a file “main.py” as follows:

main.py

from fasthtml.common import *

app,rt = fast_app()

@rt('/')
def get(): return Div(P('Hello World!'), hx_get="/change")

serve()

Running the app with python main.py prints out a link to your running
app: http://localhost:5001. Visit that link in your browser and you
should see a page with the text “Hello World!”. Congratulations, you’ve
just created your first FastHTML app!

Adding interactivity is surprisingly easy, thanks to HTMX. Modify the
file to add this function:

main.py

@rt('/change')
def get(): return P('Nice to be here!')

You now have a page with a clickable element that changes the text when
clicked. When clicking on this link, the server will respond with an
“HTML partial”—that is, just a snippet of HTML which will be inserted
into the existing page. In this case, the returned element will replace
the original P element (since that’s the default behavior of HTMX) with
the new version returned by the second route.

This “hypermedia-based” approach to web development is a powerful way to
build web applications.

Next Steps

Start with the official sources to learn more about FastHTML:

• About: Learn about the core ideas behind
  FastHTML
• Documentation: Learn from examples how to
  write FastHTML code
• Idiomatic
  app:
  Heavily commented source code walking through a complete application,
  including custom authentication, JS library connections, and database
  use.

We also have a 1-hour intro video:

https://www.youtube.com/embed/Auqrm7WFc0I

The capabilities of FastHTML are vast and growing, and not all the
features and patterns have been documented yet. Be prepared to invest
time into studying and modifying source code, such as the main FastHTML
repo’s notebooks and the official FastHTML examples repo:

• FastHTML Examples Repo on
  GitHub
• FastHTML Repo on GitHub

Then explore the small but growing third-party ecosystem of FastHTML
tutorials, notebooks, libraries, and components:

• Creating Custom FastHTML Tags for Markdown
  Rendering
  by Isaac Flath
• Your tutorial here!

Finally, join the FastHTML community to ask questions, share your work,
and learn from others:

• Discord

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