docs/ref/concise_guide.html.md

# Concise reference


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## About FastHTML

``` python
from fasthtml.common import *
```

FastHTML is a python library which brings together Starlette, Uvicorn,
HTMX, and fastcore’s `FT` “FastTags” into a library for creating
server-rendered hypermedia applications. The
[`FastHTML`](https://www.fastht.ml/docs/api/core.html#fasthtml) class
itself inherits from `Starlette`, and adds decorator-based routing with
many additions, Beforeware, automatic `FT` to HTML rendering, and much
more.

Things to remember when writing FastHTML apps:

- *Not* compatible with FastAPI syntax; FastHTML is for HTML-first apps,
  not API services (although it can implement APIs too)
- FastHTML includes support for Pico CSS and the fastlite sqlite
  library, although using both are optional; sqlalchemy can be used
  directly or via the fastsql library, and any CSS framework can be
  used. MonsterUI is a richer FastHTML-first component framework with
  similar capabilities to shadcn
- FastHTML is compatible with JS-native web components and any vanilla
  JS library, but not with React, Vue, or Svelte
- Use [`serve()`](https://www.fastht.ml/docs/api/core.html#serve) for
  running uvicorn (`if __name__ == "__main__"` is not needed since it’s
  automatic)
- When a title is needed with a response, use
  [`Titled`](https://www.fastht.ml/docs/api/xtend.html#titled); note
  that that already wraps children in
  [`Container`](https://www.fastht.ml/docs/api/pico.html#container), and
  already includes both the meta title as well as the H1 element.

## Minimal App

The code examples here use fast.ai style: prefer ternary op, 1-line
docstring, minimize vertical space, etc. (Normally fast.ai style uses
few if any comments, but they’re added here as documentation.)

A minimal FastHTML app looks something like this:

``` python
# Meta-package with all key symbols from FastHTML and Starlette. Import it like this at the start of every FastHTML app.
from fasthtml.common import *
# The FastHTML app object and shortcut to `app.route`
app,rt = fast_app()

# Enums constrain the values accepted for a route parameter
name = str_enum('names', 'Alice', 'Bev', 'Charlie')

# Passing a path to `rt` is optional. If not passed (recommended), the function name is the route ('/foo')
# Both GET and POST HTTP methods are handled by default
# Type-annotated params are passed as query params (recommended) unless a path param is defined (which it isn't here)
@rt
def foo(nm: name):
    # `Title` and `P` here are FastTags: direct m-expression mappings of HTML tags to Python functions with positional and named parameters. All standard HTML tags are included in the common wildcard import.
    # When a tuple is returned, this returns concatenated HTML partials. HTMX by default will use a title HTML partial to set the current page name. HEAD tags (e.g. Meta, Link, etc) in the returned tuple are automatically placed in HEAD; everything else is placed in BODY.
    # FastHTML will automatically return a complete HTML document with appropriate headers if a normal HTTP request is received. For an HTMX request, however, just the partials are returned.
    return Title("FastHTML"), H1("My web app"), P(f"Hello, {name}!")
# By default `serve` runs uvicorn on port 5001. Never write `if __name__ == "__main__"` since `serve` checks it internally.
serve()
```

To run this web app:

``` bash
python main.py  # access via localhost:5001
```

## FastTags (aka FT Components or FTs)

FTs are m-expressions plus simple sugar. Positional params map to
children. Named parameters map to attributes. Aliases must be used for
Python reserved words.

``` python
tags = Title("FastHTML"), H1("My web app"), P(f"Let's do this!", cls="myclass")
tags
```

    (title(('FastHTML',),{}),
     h1(('My web app',),{}),
     p(("Let's do this!",),{'class': 'myclass'}))

This example shows key aspects of how FTs handle attributes:

``` python
Label(
    "Choose an option", 
    Select(
        Option("one", value="1", selected=True),  # True renders just the attribute name
        Option("two", value=2, selected=False),   # Non-string values are converted to strings. False omits the attribute entirely
        cls="selector", id="counter",             # 'cls' becomes 'class'
        **{'@click':"alert('Clicked');"},         # Dict unpacking for attributes with special chars
    ),
    _for="counter",                               # '_for' becomes 'for' (can also use 'fr')
)
```

Classes with `__ft__` defined are rendered using that method.

``` python
class FtTest:
    def __ft__(self): return P('test')
    
to_xml(FtTest())
```

    '<p>test</p>\n'

You can create new FTs by importing the new component from
`fasthtml.components`. If the FT doesn’t exist within that module,
FastHTML will create it.

``` python
from fasthtml.components import Some_never_before_used_tag

Some_never_before_used_tag()
```

``` html
<some-never-before-used-tag></some-never-before-used-tag>
```

FTs can be combined by defining them as a function.

``` python
def Hero(title, statement): return Div(H1(title),P(statement), cls="hero")
to_xml(Hero("Hello World", "This is a hero statement"))
```

    '<div class="hero">\n  <h1>Hello World</h1>\n  <p>This is a hero statement</p>\n</div>\n'

When handling a response, FastHTML will automatically render FTs using
the `to_xml` function.

``` python
to_xml(tags)
```

    '<title>FastHTML</title>\n<h1>My web app</h1>\n<p class="myclass">Let&#x27;s do this!</p>\n'

## JS

The [`Script`](https://www.fastht.ml/docs/api/xtend.html#script)
function allows you to include JavaScript. You can use Python to
generate parts of your JS or JSON like this:

``` python
# In future snippets this import will not be shown, but is required
from fasthtml.common import * 
app,rt = fast_app(hdrs=[Script(src="https://cdn.plot.ly/plotly-2.32.0.min.js")])
# `index` is a special function name which maps to the `/` route. 
@rt
def index():
    data = {'somedata':'fill me in…'}
    # `Titled` returns a title tag and an h1 tag with the 1st param, with remaining params as children in a `Main` parent.
    return Titled("Chart Demo", Div(id="myDiv"), Script(f"var data = {data}; Plotly.newPlot('myDiv', data);"))
# In future snippets `serve() will not be shown, but is required
serve()
```

Prefer Python whenever possible over JS. Never use React or shadcn.

## fast_app hdrs

``` python
# In future snippets we'll skip showing the `fast_app` call if it has no params
app, rt = fast_app(
    pico=False, # The Pico CSS framework is included by default, so pass `False` to disable it if needed. No other CSS frameworks are included.
    # These are added to the `head` part of the page for non-HTMX requests.
    hdrs=(
        Link(rel='stylesheet', href='assets/normalize.min.css', type='text/css'),
        Link(rel='stylesheet', href='assets/sakura.css', type='text/css'),
        Style("p {color: red;}"),
        # `MarkdownJS` and `HighlightJS` are available via concise functions
        MarkdownJS(), HighlightJS(langs=['python', 'javascript', 'html', 'css']),
        # by default, all standard static extensions are served statically from the web app dir,
        #   which can be modified using e.g `static_path='public'`
        )
)

@rt
def index(req): return Titled("Markdown rendering example",
                              # This will be client-side rendered to HTML with highlight-js
                              Div("*hi* there",cls="marked"),
                              # This will be syntax highlighted
                              Pre(Code("def foo(): pass")))
```

## Responses

Routes can return various types:

1.  FastTags or tuples of FastTags (automatically rendered to HTML)
2.  Standard Starlette responses (used directly)
3.  JSON-serializable types (returned as JSON in a plain text response)

``` python
@rt("/{fname:path}.{ext:static}")
async def serve_static_file(fname:str, ext:str): return FileResponse(f'public/{fname}.{ext}')

app, rt = fast_app(hdrs=(MarkdownJS(), HighlightJS(langs=['python', 'javascript'])))
@rt
def index(): 
    return Titled("Example",
                  Div("*markdown* here", cls="marked"),
                  Pre(Code("def foo(): pass")))
```

Route functions can be used in attributes like `href` or `action` and
will be converted to paths. Use `.to()` to generate paths with query
parameters.

``` python
@rt
def profile(email:str): return fill_form(profile_form, profiles[email])

profile_form = Form(action=profile)(
    Label("Email", Input(name="email")),
    Button("Save", type="submit")
)

user_profile_path = profile.to(email="[email protected]")  # '/profile?email=user%40example.com'
```

``` python
from dataclasses import dataclass

app,rt = fast_app()
```

When a route handler function is used as a fasttag attribute (such as
`href`, `hx_get`, or `action`) it is converted to that route’s path.
[`fill_form`](https://www.fastht.ml/docs/api/components.html#fill_form)
is used to copy an object’s matching attrs into matching-name form
fields.

``` python
@dataclass
class Profile: email:str; phone:str; age:int
email = '[email protected]'
profiles = {email: Profile(email=email, phone='123456789', age=5)}
@rt
def profile(email:str): return fill_form(profile_form, profiles[email])

profile_form = Form(method="post", action=profile)(
        Fieldset(
            Label('Email', Input(name="email")),
            Label("Phone", Input(name="phone")),
            Label("Age", Input(name="age"))),
        Button("Save", type="submit"))
```

## Testing

We can use `TestClient` for testing.

``` python
from starlette.testclient import TestClient
```

``` python
path = "/[email protected]"
client = TestClient(app)
htmx_req = {'HX-Request':'1'}
print(client.get(path, headers=htmx_req).text)
```

    <form enctype="multipart/form-data" method="post" action="/profile"><fieldset><label>Email       <input name="email" value="[email protected]">
    </label><label>Phone       <input name="phone" value="123456789">
    </label><label>Age       <input name="age" value="5">
    </label></fieldset><button type="submit">Save</button></form>

## Form Handling and Data Binding

When a dataclass, namedtuple, etc. is used as a type annotation, the
form body will be unpacked into matching attribute names automatically.

``` python
@rt
def edit_profile(profile: Profile):
    profiles[email]=profile
    return RedirectResponse(url=path)

new_data = dict(email='[email protected]', phone='7654321', age=25)
print(client.post("/edit_profile", data=new_data, headers=htmx_req).text)
```

    <form enctype="multipart/form-data" method="post" action="/profile"><fieldset><label>Email       <input name="email" value="[email protected]">
    </label><label>Phone       <input name="phone" value="7654321">
    </label><label>Age       <input name="age" value="25">
    </label></fieldset><button type="submit">Save</button></form>

## fasttag Rendering Rules

The general rules for rendering children inside tuples or fasttag
children are: - `__ft__` method will be called (for default components
like `P`, `H2`, etc. or if you define your own components) - If you pass
a string, it will be escaped - On other python objects, `str()` will be
called

If you want to include plain HTML tags directly into e.g. a `Div()` they
will get escaped by default (as a security measure to avoid code
injections). This can be avoided by using `Safe(...)`, e.g to show a
data frame use `Div(NotStr(df.to_html()))`.

## Exceptions

FastHTML allows customization of exception handlers.

``` python
def not_found(req, exc): return Titled("404: I don't exist!")
exception_handlers = {404: not_found}
app, rt = fast_app(exception_handlers=exception_handlers)
```

## Cookies

We can set cookies using the
[`cookie()`](https://www.fastht.ml/docs/api/core.html#cookie) function.

``` python
@rt
def setcook(): return P(f'Set'), cookie('mycookie', 'foobar')
print(client.get('/setcook', headers=htmx_req).text)
```

     <p>Set</p>

``` python
@rt
def getcook(mycookie:str): return f'Got {mycookie}'
# If handlers return text instead of FTs, then a plaintext response is automatically created
print(client.get('/getcook').text)
```

    Got foobar

FastHTML provide access to Starlette’s request object automatically
using special `request` parameter name (or any prefix of that name).

``` python
@rt
def headers(req): return req.headers['host']
```

## Request and Session Objects

FastHTML provides access to Starlette’s session middleware automatically
using the special `session` parameter name (or any prefix of that name).

``` python
@rt
def profile(req, sess, user_id: int=None):
    ip = req.client.host
    sess['last_visit'] = datetime.now().isoformat()
    visits = sess.setdefault('visit_count', 0) + 1
    sess['visit_count'] = visits
    user = get_user(user_id or sess.get('user_id'))
    return Titled(f"Profile: {user.name}", 
                  P(f"Visits: {visits}"), 
                  P(f"IP: {ip}"),
                  Button("Logout", hx_post=logout))
```

Handler functions can return the
[`HtmxResponseHeaders`](https://www.fastht.ml/docs/api/core.html#htmxresponseheaders)
object to set HTMX-specific response headers.

``` python
@rt
def htmlredirect(app): return HtmxResponseHeaders(location="http://example.org")
```

## APIRouter

[`APIRouter`](https://www.fastht.ml/docs/api/core.html#apirouter) lets
you organize routes across multiple files in a FastHTML app.

``` python
# products.py
ar = APIRouter()

@ar
def details(pid: int): return f"Here are the product details for ID: {pid}"

@ar
def all_products(req):
    return Div(
        Div(
            Button("Details",hx_get=details.to(pid=42),hx_target="#products_list",hx_swap="outerHTML",),
        ), id="products_list")
```

``` python
# main.py
from products import ar,all_products

app, rt = fast_app()
ar.to_app(app)

@rt
def index():
    return Div(
        "Products",
        hx_get=all_products, hx_swap="outerHTML")
```

## Toasts

Toasts can be of four types:

- info
- success
- warning
- error

Toasts require the use of the `setup_toasts()` function, plus every
handler needs:

- The session argument
- Must return FT components

``` python
setup_toasts(app)

@rt
def toasting(session):
    add_toast(session, f"cooked", "info")
    add_toast(session, f"ready", "success")
    return Titled("toaster")
```

`setup_toasts(duration)` allows you to specify how long a toast will be
visible before disappearing.10 seconds.

Authentication and authorization are handled with Beforeware, which
functions that run before the route handler is called.

## Auth

``` python
def user_auth_before(req, sess):
    # `auth` key in the request scope is automatically provided to any handler which requests it and can not be injected
    auth = req.scope['auth'] = sess.get('auth', None)
    if not auth: return RedirectResponse('/login', status_code=303)

beforeware = Beforeware(
    user_auth_before,
    skip=[r'/favicon\.ico', r'/static/.*', r'.*\.css', r'.*\.js', '/login', '/']
)

app, rt = fast_app(before=beforeware)
```

## Server-Side Events (SSE)

FastHTML supports the HTMX SSE extension.

``` python
import random
hdrs=(Script(src="https://unpkg.com/[email protected]/sse.js"),)
app,rt = fast_app(hdrs=hdrs)

@rt
def index(): return Div(hx_ext="sse", sse_connect="/numstream", hx_swap="beforeend show:bottom", sse_swap="message")

# `signal_shutdown()` gets an event that is set on shutdown
shutdown_event = signal_shutdown()

async def number_generator():
    while not shutdown_event.is_set():
        data = Article(random.randint(1, 100))
        yield sse_message(data)

@rt
async def numstream(): return EventStream(number_generator())
```

## Websockets

FastHTML provides useful tools for HTMX’s websockets extension.

``` python
# These HTMX extensions are available through `exts`:
#   head-support preload class-tools loading-states multi-swap path-deps remove-me ws chunked-transfer
app, rt = fast_app(exts='ws')

def mk_inp(): return Input(id='msg', autofocus=True)

@rt
async def index(request):
    # `ws_send` tells HTMX to send a message to the nearest websocket based on the trigger for the form element
    cts = Div(
        Div(id='notifications'),
        Form(mk_inp(), id='form', ws_send=True),
        hx_ext='ws', ws_connect='/ws')
    return Titled('Websocket Test', cts)

async def on_connect(send): await send(Div('Hello, you have connected', id="notifications"))
async def on_disconnect(ws): print('Disconnected!')

@app.ws('/ws', conn=on_connect, disconn=on_disconnect)
async def ws(msg:str, send):
    # websocket hander returns/sends are treated as OOB swaps
    await send(Div('Hello ' + msg, id="notifications"))
    return Div('Goodbye ' + msg, id="notifications"), mk_inp()
```

Sample chatbot that uses FastHTML’s
[`setup_ws`](https://www.fastht.ml/docs/api/core.html#setup_ws)
function:

``` py
app = FastHTML(exts='ws')
rt = app.route
msgs = []

@rt('/')
def home():
    return Div(hx_ext='ws', ws_connect='/ws')(
        Div(Ul(*[Li(m) for m in msgs], id='msg-list')),
        Form(Input(id='msg'), id='form', ws_send=True)
    )

async def ws(msg:str):
    msgs.append(msg)
    await send(Ul(*[Li(m) for m in msgs], id='msg-list'))

send = setup_ws(app, ws)
```

### Single File Uploads

[`Form`](https://www.fastht.ml/docs/api/xtend.html#form) defaults to
“multipart/form-data”. A Starlette UploadFile is passed to the handler.

``` python
upload_dir = Path("filez")

@rt
def index():
    return (
        Form(hx_post=upload, hx_target="#result")(
            Input(type="file", name="file"),
            Button("Upload", type="submit")),
        Div(id="result")
    )

# Use `async` handlers where IO is used to avoid blocking other clients
@rt
async def upload(file: UploadFile):
    filebuffer = await file.read()
    (upload_dir / file.filename).write_bytes(filebuffer)
    return P('Size: ', file.size)
```

For multi-file, use `Input(..., multiple=True)`, and a type annotation
of `list[UploadFile]` in the handler.

## Fastlite

Fastlite and the MiniDataAPI specification it’s built on are a
CRUD-oriented API for working with SQLite. APSW and apswutils is used to
connect to SQLite, optimized for speed and clean error handling.

``` python
from fastlite import *
```

``` python
db = database(':memory:') # or database('data/app.db')
```

Tables are normally constructed with classes, field types are specified
as type hints.

``` python
class Book: isbn: str; title: str; pages: int; userid: int
# The transform arg instructs fastlite to change the db schema when fields change.
# Create only creates a table if the table doesn't exist.
books = db.create(Book, pk='isbn', transform=True)
                
class User: id: int; name: str; active: bool = True
# If no pk is provided, id is used as the primary key.
users = db.create(User, transform=True)
users
```

    <Table user (id, name, active)>

### Fastlite CRUD operations

Every operation in fastlite returns a full superset of dataclass
functionality.

``` python
user = users.insert(name='Alex',active=False)
user
```

    User(id=1, name='Alex', active=0)

``` python
# List all records
users()
```

    [User(id=1, name='Alex', active=0)]

``` python
# Limit, offset, and order results:
users(order_by='name', limit=2, offset=1)

# Filter on the results
users(where="name='Alex'")

# Placeholder for avoiding injection attacks
users("name=?", ('Alex',))

# A single record by pk
users[user.id]
```

    User(id=1, name='Alex', active=0)

Test if a record exists by using `in` keyword on primary key:

``` python
1 in users
```

    True

Updates (which take a dict or a typed object) return the updated record.

``` python
user.name='Lauren'
user.active=True
users.update(user)
```

    User(id=1, name='Lauren', active=1)

`.xtra()` to automatically constrain queries, updates, and inserts from
there on:

``` python
users.xtra(active=True)
users()
```

    [User(id=1, name='Lauren', active=1)]

Deleting by pk:

``` python
users.delete(user.id)
```

    <Table user (id, name, active)>

NotFoundError is raised by pk `[]`, updates, and deletes.

``` python
try: users['Amy']
except NotFoundError: print('User not found')
```

    User not found

## MonsterUI

MonsterUI is a shadcn-like component library for FastHTML. It adds the
Tailwind-based libraries FrankenUI and DaisyUI to FastHTML, as well as
Python’s mistletoe for Markdown, HighlightJS for code highlighting, and
Katex for latex support, following semantic HTML patterns when possible.
It is recommended for when you wish to go beyond the basics provided by
FastHTML’s built-in pico support.

A minimal app:

``` python
from fasthtml.common import *
from monsterui.all import *

app, rt = fast_app(hdrs=Theme.blue.headers(highlightjs=True)) # Use MonsterUI blue theme and highlight code in markdown

@rt
def index():
    socials = (('github','https://github.com/AnswerDotAI/MonsterUI'),)
    return Titled("App",
        Card(
            P("App", cls=TextPresets.muted_sm),
            # LabelInput, DivLAigned, and UkIconLink are non-semantic MonsterUI FT Components,
            LabelInput('Email', type='email', required=True),
            footer=DivLAligned(*[UkIconLink(icon,href=url) for icon,url in socials])))
```

MonsterUI recommendations:

- Use defaults as much as possible, for example
  [`Container`](https://www.fastht.ml/docs/api/pico.html#container) in
  monsterui already has defaults for margins
- Use `*T` for button styling consistency, for example
  `cls=ButtonT.destructive` for a red delete button or
  `cls=ButtonT.primary` for a CTA button
- Use `Label*` functions for forms as much as possible
  (e.g. `LabelInput`, `LabelRange`) which creates and links both the
  `FormLabel` and user input appropriately to avoid boiler plate.

Flex Layout Elements (such as `DivLAligned` and `DivFullySpaced`) can be
used to create layouts concisely

``` python
def TeamCard(name, role, location="Remote"):
    icons = ("mail", "linkedin", "github")
    return Card(
        DivLAligned(
            DiceBearAvatar(name, h=24, w=24),
            Div(H3(name), P(role))),
        footer=DivFullySpaced(
            DivHStacked(UkIcon("map-pin", height=16), P(location)),
            DivHStacked(*(UkIconLink(icon, height=16) for icon in icons))))
```

Forms are styled and spaced for you without significant additional
classes.

``` python
def MonsterForm():
    relationship = ["Parent",'Sibling', "Friend", "Spouse", "Significant Other", "Relative", "Child", "Other"]
    return Div(
        DivCentered(
            H3("Emergency Contact Form"),
            P("Please fill out the form completely", cls=TextPresets.muted_sm)),
        Form(
            Grid(LabelInput("Name",id='name'),LabelInput("Email",     id='email')),
            H3("Relationship to patient"),
            Grid(*[LabelCheckboxX(o) for o in relationship], cols=4, cls='space-y-3'),
            DivCentered(Button("Submit Form", cls=ButtonT.primary))),
        cls='space-y-4')
```

Text can be styled with markdown automatically with MonsterUI

```` python
render_md("""
# My Document

> Important note here

+ List item with **bold**
+ Another with `code`

```python
def hello():
    print("world")
```
""")
````

    '<div><h1 class="uk-h1 text-4xl font-bold mt-12 mb-6">My Document</h1>\n<blockquote class="uk-blockquote pl-4 border-l-4 border-primary italic mb-6">\n<p class="text-lg leading-relaxed mb-6">Important note here</p>\n</blockquote>\n<ul class="uk-list uk-list-bullet space-y-2 mb-6 ml-6 text-lg">\n<li class="leading-relaxed">List item with <strong>bold</strong></li>\n<li class="leading-relaxed">Another with <code class="uk-codespan px-1">code</code></li>\n</ul>\n<pre class="bg-base-200 rounded-lg p-4 mb-6"><code class="language-python uk-codespan px-1 uk-codespan px-1 block overflow-x-auto">def hello():\n    print("world")\n</code></pre>\n</div>'

Or using semantic HTML:

``` python
def SemanticText():
    return Card(
        H1("MonsterUI's Semantic Text"),
        P(
            Strong("MonsterUI"), " brings the power of semantic HTML to life with ",
            Em("beautiful styling"), " and ", Mark("zero configuration"), "."),
        Blockquote(
            P("Write semantic HTML in pure Python, get modern styling for free."),
            Cite("MonsterUI Team")),
        footer=Small("Released February 2025"),)
```