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FastAPI and HTMX, the right way.

Key features:

  • Decorator syntax that works with FastAPI as one would expect, no need for unused or magic dependencies in routes.
  • Works with any templating engine or server-side rendering library, e.g. markyp-html or dominate.
  • Built-in Jinja2 templating support (even with multiple template folders).
  • Gives the rendering engine access to all dependencies of the decorated route.
  • FastAPI routes will keep working normally by default if they receive non-HTMX requests, so the same route can serve data and render HTML at the same time.
  • Response headers you set in your routes are kept after rendering, as you would expect in FastAPI.
  • Correct typing makes it possible to apply other (typed) decorators to your routes.
  • Works with both sync and async routes.


The package is available on PyPI and can be installed with:

$ pip install fasthx


For complete, but simple examples that showcase the basic use of FastHX, please see the examples folder.

If you're looking for a more complex (Jinja2) example with features like active search, lazy-loading, server-sent events, custom server-side HTMX triggers, dialogs, and TailwindCSS and DaisyUI integration, check out this FastAPI-HTMX-Tailwind example.

Jinja2 templating

To start serving HTML and HTMX requests, all you need to do is create an instance of fasthx.Jinja and use its hx() or page() methods as decorators on your routes. hx() only triggers HTML rendering for HTMX requests, while page() unconditionally renders HTML, saving you some boilerplate code. See the example code below:

from fastapi import FastAPI
from fastapi.templating import Jinja2Templates
from fasthx import Jinja
from pydantic import BaseModel

# Pydantic model of the data the example API is using.
class User(BaseModel):
    first_name: str
    last_name: str

# Create the app.
app = FastAPI()

# Create a FastAPI Jinja2Templates instance and use it to create a
# FastHX Jinja instance that will serve as your decorator.
jinja = Jinja(Jinja2Templates("templates"))

def index() -> None:

async def htmx_or_data() -> list[User]:
    return [
        User(first_name="John", last_name="Lennon"),
        User(first_name="Paul", last_name="McCartney"),
        User(first_name="George", last_name="Harrison"),
        User(first_name="Ringo", last_name="Starr"),

@jinja.hx("user-list.html", no_data=True)
def htmx_only() -> list[User]:
    return [User(first_name="Billy", last_name="Shears")]

Custom templating

If you're not into Jinja templating, the hx() and page() decorators give you all the flexibility you need: you can integrate any HTML rendering or templating engine into fasthx simply by implementing the HTMLRenderer protocol. Similarly to the Jinja case, hx() only triggers HTML rendering for HTMX requests, while page() unconditionally renders HTML. See the example code below:

from typing import Annotated, Any

from fastapi import Depends, FastAPI, Request
from fasthx import hx, page

# Create the app.
app = FastAPI()

# Create a dependecy to see that its return value is available in the render function.
def get_random_number() -> int:
    return 4  # Chosen by fair dice roll.

DependsRandomNumber = Annotated[int, Depends(get_random_number)]

# Create the render methods: they must always have these three arguments.
# If you're using static type checkers, the type hint of `result` must match
# the return type annotation of the route on which this render method is used.
def render_index(result: list[dict[str, str]], *, context: dict[str, Any], request: Request) -> str:
    return "<h1>Hello FastHX</h1>"

def render_user_list(result: list[dict[str, str]], *, context: dict[str, Any], request: Request) -> str:
    # The value of the `DependsRandomNumber` dependency is accessible with the same name as in the route.
    random_number = context["random_number"]
    lucky_number = f"<h1>{random_number}</h1>"
    users = "".join(("<ul>", *(f"<li>{u['name']}</li>" for u in result), "</ul>"))
    return f"{lucky_number}\n{users}"

def index() -> None:

def htmx_or_data(random_number: DependsRandomNumber) -> list[dict[str, str]]:
    return [{"name": "Joe"}]

@hx(render_user_list, no_data=True)
async def htmx_only(random_number: DependsRandomNumber) -> list[dict[str, str]]:
    return [{"name": "Joe"}]


The only dependency of this package is fastapi.


Use ruff for linting and formatting, mypy for static code analysis, and pytest for testing.

The documentation is built with mkdocs-material and mkdocstrings.


All contributions are welcome.

License - MIT

The package is open-sourced under the conditions of the MIT license.