ztml 0.2.3

Rust-backed framework for building websites in pure Python

ztml

A Rust-backed framework for building websites in pure Python. ZTML allows you to define HTML/CSS/JS using only Python expressions with as much autocompletion support as I could reasonably add. Inspired by FastHTML.

Install

pip install ztml

HTML

Every HTML element has a corresponding constructor function. Attributes are set via chained builder methods. Call render() to get an HTML string.

from ztml import *

page = render(
    Html(
        Head(Meta().charset("utf-8"), Title("My App")),
        Body(
            H1("Hello, ztml!"),
            P("Build websites with Python.").cls("intro"),
            A("GitHub").href("https://github.com").target("_blank"),
        ),
    )
)

Attributes chain naturally:

Div(
    Input().type("text").name("q").placeholder("Search...").autofocus(),
    Button("Go").type("submit"),
).cls("search-box").id("search")

Use Fragment to group elements without a wrapper tag, and Raw to inject unescaped HTML:

Fragment(
    H1("Title"),
    P("Paragraph"),
    Raw("<hr/>"),
)

Style

Build CSS with Rule, Media, Keyframes, and Frame. Wrap them in Style() to render a <style> block.

Style(
    Rule("body").margin("0").font_family("system-ui, sans-serif"),
    Rule(".container").display("flex").gap("1rem").padding("2rem"),
    Rule(".container > .sidebar").width("250px").flex_shrink("0"),
    Rule(".container > .main").flex("1"),

    Media("max-width: 768px",
        Rule(".container").flex_direction("column"),
        Rule(".container > .sidebar").width("100%"),
    ),

    Keyframes("fadeIn",
        Frame("from").opacity("0").transform("translateY(-10px)"),
        Frame("to").opacity("1").transform("translateY(0)"),
    ),

    Rule(".card").animation("fadeIn 0.3s ease-out"),
)

CSS property methods are generated from W3C specs — every standard property is available with autocompletion. Use .prop("custom-property", "value") for anything not covered.

Inline styles work too:

Div("styled").style(InlineStyle().color("red").font_weight("bold"))

Script

Build JavaScript with On event handlers and RawJs. Wrap them in Script() to render a <script> block.

Script(
    On.click("#increment", """
        let count = document.getElementById('count');
        count.textContent = parseInt(count.textContent) + 1;
    """),

    On.document_ready("console.log('page loaded')"),

    On.submit("#my-form", """
        event.preventDefault();
        alert('submitted!');
    """),

    RawJs("function greet(name) { alert('Hello, ' + name); }"),
)

Available event helpers: On.click, On.submit, On.change, On.input, On.keydown, On.keyup, On.mouseover, On.mouseout, On.focus, On.blur, On.document_ready, and On.event for custom events.

Custom Components

Any Python object with a __ztml_render__ method can be used as a renderable component. The method should return a ztml element.

class Card:
    def __init__(self, title, body):
        self.title = title
        self.body = body

    def __ztml_render__(self):
        return Div(
            H2(self.title),
            P(self.body),
        ).cls("card")

# Use directly in render()
print(render(Card("Hello", "World")))

# Or nest inside other elements
page = Div(
    Card("First", "Some content"),
    Card("Second", "More content"),
).cls("cards")

Jupyter & Jinja2 Compatibility

All built-in ztml elements implement _repr_html_() (for Jupyter notebook display) and __html__() (for Jinja2/MarkupSafe auto-escaping). Evaluating an element at the end of a Jupyter cell will render it as HTML automatically.

For custom components, add these methods using render():

class Card:
    def __init__(self, title, body):
        self.title = title
        self.body = body

    def __ztml_render__(self):
        return Div(H2(self.title), P(self.body)).cls("card")

    def __html__(self):
        return render(self)

    def _repr_html_(self):
        return render(self)

Putting It Together

A complete page with HTML, CSS, and JS:

from ztml import *

def page():
    return Html(
        Head(
            Meta().charset("utf-8"),
            Title("Counter"),
            Style(
                Rule("body").font_family("system-ui").display("flex")
                    .justify_content("center").padding("4rem"),
                Rule("button").padding("0.5rem 1rem").font_size("1.2rem")
                    .cursor("pointer").border_radius("4px"),
                Rule("#count").font_size("3rem").margin("1rem 0"),
            ),
        ),
        Body(
            H1("Counter"),
            P("0").id("count"),
            Button("Increment").id("increment"),
            Script(
                On.click("#increment", """
                    let el = document.getElementById('count');
                    el.textContent = parseInt(el.textContent) + 1;
                """),
            ),
        ),
    )

print(render(page()))

Server

ztml includes a built-in server for HTMX-powered apps, built on Starlette and Uvicorn.

from ztml import *
from ztml.scripts import HTMX
from ztml.server import rt, serve

@rt('/')
def get():
    return Html(
        Head(Title("Counter"), HTMX),
        Body(
            H1("Counter"),
            P("0").id("count"),
            Button("Increment").hx_post("/increment").hx_target("#count"),
        ),
    )

count = 0

@rt('/increment')
def post():
    global count
    count += 1
    return P(str(count)).id("count")

serve()  # localhost:5001

Key features:

• Method inference — HTTP method inferred from function name (get, post, put, delete, etc.)
• Path parameters — @rt('/greet/{name}') extracts name as a function argument
• Request access — add request to access the Starlette Request object
• Element rendering — return ztml elements, automatically rendered to HTML

Form Data & File Uploads

Name a parameter form_data or files and it's automatically parsed:

@rt('/submit', methods=['POST'])
async def submit(form_data):
    name = form_data['name']
    return Div(f"Hello, {name}")

Sessions

Pass session_secret to enable cookie-backed sessions. Add session to any handler signature:

from ztml.server import ZTMLApp, serve

app = ZTMLApp(session_secret="your-secret-key")

@app.route('/login', methods=['POST'])
def login(session, form_data):
    session['user'] = form_data['username']
    return Div("Logged in")

@app.route('/profile')
def profile(session):
    return Div(f"Hello, {session.get('user', 'guest')}")

serve(target=app)

For raw cookies (outside of sessions), use Starlette's built-in response.set_cookie() and request.cookies.get().

Before Hooks

Run checks before a route handler executes. Return a Response to short-circuit:

from starlette.responses import RedirectResponse

def require_auth(session):
    if not session.get('user'):
        return RedirectResponse('/login', status_code=303)

@app.route('/dashboard', before=[require_auth])
def dashboard(session):
    return Div(f"Welcome, {session['user']}")

Live Reload

Set dev=True to enable uvicorn file-watching and automatic browser refresh on save:

app = ZTMLApp(dev=True)
# serve() automatically passes reload=True to uvicorn in dev mode

WebSockets & SSE

from ztml.server import ZTMLApp, EventStream

app = ZTMLApp()

@app.ws('/echo')
async def echo(websocket):
    await websocket.accept()
    data = await websocket.receive_text()
    await websocket.send_text(f"echo: {data}")
    await websocket.close()

@app.route('/stream')
async def get():
    async def updates():
        yield Div("first update")
        yield Div("second update")
    return EventStream(updates()).response()

Building from Source

Prerequisites: Rust toolchain, Python 3.12+, uv.

# Install dependencies and build the Rust extension
uv sync

# For iterative development (faster rebuilds)
uv run maturin develop

# Generate .pyi type stubs for autocompletion
cargo run --bin gen_stubs --no-default-features

To build a distributable wheel:

maturin build --release
# Output in target/wheels/

Examples

# Generate a static HTML page to stdout 
uv run examples/static_page.py > page.html # (open page.html in your browser!)

# HTMX counter app (localhost:5001)
uv run examples/counter_server.py

# Custom components demo
uv run examples/components.py > components.html

# HTMX todo app (localhost:5001)
uv run examples/todo_server.py

# Auth demo with sessions & before hooks (localhost:5001)
uv run examples/auth_app.py

# WebSocket chat room (localhost:5001)
uv run examples/ws_chat.py

# SSE live clock (localhost:5001)
uv run examples/sse_clock.py

Benchmarks

Compared against FastHTML building and rendering nested HTML element trees:

Scenario         Library      Elements   Build (ms)   Render (ms)   Total (ms)
---------------------------------------------------------------------------
10x50            ztml             1040         1.44          0.09         1.54
10x50            fasthtml         1040        14.72          2.62        17.35
                             speedup: build 10.2x, render 28.5x, total 11.3x

50x100           ztml            10200        14.65          0.90        15.55
50x100           fasthtml        10200       151.36         26.12       177.61
                             speedup: build 10.3x, render 28.9x, total 11.4x

100x200          ztml            40400        58.04          3.63        61.69
100x200          fasthtml        40400       710.79        106.00       816.57
                             speedup: build 12.2x, render 29.2x, total 13.2x

^ M3 Pro MacBook Pro

Run the benchmark yourself:

uv pip install python-fasthtml
uv run benchmarks/bench.py

Running Tests

uv run python -m pytest

# Rust unit tests
cargo test -p ztml-core

How codegen works

build.rs reads HTML element definitions from webtags and CSS property specs from w3c/webref, stored in specs/. From these it generates:

• Element constructors — one Python function per HTML tag
• CSS property methods — on Rule, InlineStyle, and Frame
• Enum classes — for CSS keyword values and HTML attribute values

Releasing

CI runs on every push to main and on tags matching v*.

Regular push (tests only):

git push

Publishing a new version (build + publish to PyPI):

1. Bump the version in crates/ztml-core/Cargo.toml and crates/ztml-python/Cargo.toml
2. Commit, tag, and push:

git add -A && git commit -m "bump version to 0.x.y"
git tag v0.x.y
git push && git push origin v0.x.y

The v* tag triggers the full build matrix (Linux, macOS, Windows) and publishes wheels to PyPI via trusted publishing.

License

MIT