Koyo

Koyo is a Python web framework that mirrors the developer experience of Next.js (the app directory convention, file based routing, layouts, reusable components) but is written entirely in Python and runs as a normal Python web server. Since it is a normal Python process under the hood, any package installed with pip is available immediately, with no build step or compiler touching the Python code.

This is v1, frontend and routing only. No backend API layer, no database, no auth.

Koyo is free and open source under the MIT license. Fork it, use it anywhere, for anything, and ship what you build with it. Contributions are welcome; open an issue or pull request on the repository.

Install

Koyo requires Python 3.11 or newer.

pip install koyoapp

Quickstart

koyoapp create my-app
cd my-app
koyoapp dev

Open http://127.0.0.1:2309. The home page renders out of the box with an animated hero, a call to action linking to the Koyo documentation, and a live session counter driven by htmx. Edit any file under app/, public/, or styles/ and the page updates in place without a full reload.

Deploying

Every scaffold ships deploy-ready files: a Procfile that starts python -m uvicorn koyoapp.serve:app on $PORT, a requirements.txt pinning the koyoapp release, and a .railwayignore that keeps the local venv and build output out of deploys. Railway, Render, and any Procfile based host can run a Koyo app with no extra setup; for static-only sites, koyoapp build prerenders into .koyo/build/site for any static host. See https://justphemi.github.io/koyo-docs for a full guide.

CLI

• koyoapp create . scaffolds a Koyo project into the current directory.
• koyoapp create my-app creates my-app and scaffolds inside it.
• koyoapp dev starts the dev server on port 2309 by default, override with --port. If the port is already in use, the next free port is used automatically.
• koyoapp build prerenders every static route into .koyo/build/site.

Project structure

my-app/
  app/
    layout.py
    page.py
  components/
    counter.py
    landing.py
    site.py
  public/
  styles/
  koyo.config.py
  pyproject.toml

Routing rules follow the Next.js app directory convention. Folders wrapped in square brackets become dynamic path parameters. A page file must export a function named page, and a layout file must export a function named layout(children). Layouts nest outward to inward, exactly like Next.js.

Component system

koyoapp.html exposes function based HTML elements. Text content is HTML escaped by default; use Markup (or raw()) for raw unescaped output. Children can be passed positionally as arguments or appended with square brackets; both styles can be mixed, and a list (or any iterable) passed as a single child is flattened in place. Attributes map underscores to hyphens (hx_, data_, aria_), and class_ / cls both mean class.

from koyoapp.html import div, h1, p, span

def Card(title: str, body: str):
    return div(class_="p-4 rounded-lg shadow bg-white")[
        h1(class_="text-xl font-bold")[title],
        p(class_="text-gray-600")[body],
    ]

def Row(label: str, value: str):
    return div(span(label, cls="font-medium"), span(value), class_="flex gap-2")

Styles

koyoapp dev runs the Tailwind CLI in watch mode against the project and compiles styles/globals.css to styles/koyo.css, which the root layout links automatically. Any other .css file under styles/ is served untouched from /styles/ and can be linked directly with a normal link tag. The scaffold ships a light/dark theme switch: public/theme.js applies the saved or system-preferred theme before first paint, the hero button toggles it and stores the choice in localStorage, and dark mode is class based (darkMode: "class") so any element can use dark: variants.

Packages

There is no custom package manager. Activate the project virtualenv and use plain pip:

.venv/bin/pip install <package>

The package is importable in any page.py, layout.py, or component file immediately, since Koyo runs as a normal Python process.