FluidKit

Web development for the pythoniers

FluidKit provides tooling for building modern, highly optimized fullstack web applications with Python + the power of SvelteKit. Automatic type-safe client generation and environment-aware proxying make FastAPI + SvelteKit feel like a unified framework.

pip install fluidkit

Build Modern Web Apps with Python

Access the JavaScript ecosystem for UI while keeping all your business logic in Python. No Node.js backend knowledge required.

📦 Client Generation - For any project setup

import fluidkit
fluidkit.integrate(app)  # Generates portable TypeScript clients

🌐 Full-Stack Development - Python + SvelteKit unified

import fluidkit
fluidkit.integrate(app, enable_fullstack=True)  # Complete fullstack tooling

🚀 Full-Stack Get Started

Prerequisites: Node.js, uv (preferred) or Poetry

# 1. Create SvelteKit project
npx sv create my-app
cd my-app

# 2. Initialize Python environment
uv init  # or: poetry init
uv add fluidkit  # or: poetry add fluidkit

# 3. Create Python backend

Folder structure:

src/
├── routes/
│   ├── +page.svelte  # Svelte component (frontend)
│   ├── hello.api.py  # Python API logic (backend api for the frontend)
│   └── hello.api.ts  # Auto-generated by FluidKit
└── app.py

Create src/app.py:

import fluidkit
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

fluidkit.integrate(app, enable_fullstack=True)

if __name__ == "__main__":
  import uvicorn
  uvicorn.run("app:app", host="0.0.0.0", port=8000, reload=True)

Create src/routes/hello.api.py:

from fastapi import APIRouter
from pydantic import BaseModel

router = APIRouter()

class Message(BaseModel):
    text: str

@router.get("/hello")
async def get_message() -> Message:
    return Message(text="Hello from Python!")

Use in src/routes/+page.svelte:

<script>
  import { get_message } from './hello.api';
  
  let message = $state('');
  
  get_message().then(result => {
    if (result.success) message = result.data.text;
  });
</script>

<h1>{message}</h1>

# 4. Start development
uv run python src/app.py  # Start Python backend
npm run dev  # Start SvelteKit (separate terminal)

You're ready! Visit http://localhost:5173 to see your full-stack app. Visit http://localhost:5173/proxy/docs to see fastapi swagger UI.

The FluidKit Experience

Write your backend in Python:

from uuid import UUID
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class User(BaseModel):
    id: UUID
    name: str
    email: str

@app.get("/users/{user_id}")
async def get_user(user_id: UUID) -> User:
    # Your Python logic - database, validation, etc.
    return fetch_user_from_database(user_id)

import fluidkit
fluidkit.integrate(app, enable_fullstack=True)

Use directly in SvelteKit like local functions:

<script>
  import { get_user } from './users.api';
  
  let userId = $state('');
  let user = $state(null);
  let error = $state('');
  
  function loadUser() {
    error = '';
    get_user(userId).then(result => {
      if (result.success) {
        user = result.data;
      } else {
        error = result.error;
      }
    });
  }
</script>

<input bind:value={userId} placeholder="Enter user ID" />
<button onclick={loadUser}>Load User</button>

{#if error}
  <p style="color: red;">{error}</p>
{/if}

{#if user}
  <div>
    <h3>{user.name}</h3>
    <p>{user.email}</p>
  </div>
{/if}

FluidKit automatically generates:

// Full type safety from Python → TypeScript
export interface User {
  id: FluidTypes.UUID;
  name: string;
  email: string;
}

export const get_user = async (user_id: FluidTypes.UUID): Promise<ApiResult<User>> => {
  // Environment-aware: direct FastAPI in SSR, proxied in browser
};

✨ What's New in v0.2.6

• 🔄 Streaming Support - Server-Sent Events, file downloads, JSON streaming
• 🏷️ FluidTypes Namespace - Clean handling of external types (UUID, Decimal, DateTime)
• 📁 Enhanced Auto-Discovery - SvelteKit-style folder routing with parameter validation
• ⚡ Simplified Configuration - Zero config for client generation, rich config for fullstack

🚀 Key Features

• Unified Development Experience - Write Python, get modern SvelteKit web apps
• Complete Type Safety - Python types → TypeScript interfaces automatically
• Environment-Aware Proxying - Same client works in SSR and browser seamlessly
• Streaming First-Class - SSE, file downloads, JSON streaming support
• Smart External Types - UUID, Decimal, DateTime via clean FluidTypes namespace
• Auto-Discovery - SvelteKit-style file-based routing patterns
• Zero Node.js Knowledge Required - Pure Python backend development
• Highly Optimized - SvelteKit's SSR, hydration, code splitting, and performance

🛠️ Two Development Modes

Client Generation Only

Perfect for existing projects, microservices, or when frontend/backend deploy separately:

# Generates portable TypeScript clients
fluidkit.integrate(app)

• Clean .fluidkit/ output directory
• Copy generated clients to any frontend project
• Works with React, Vue, vanilla TypeScript, etc.
• Full type safety across the API boundary

Full-Stack Development

Unified Python + SvelteKit development with seamless integration:

# Enables complete fullstack tooling
fluidkit.integrate(app, enable_fullstack=True)

• Auto-generated SvelteKit proxy routes
• Environment-aware client (SSR + browser)
• Hot reload across frontend and backend
• Production deployment optimization
• Auto-discovery of API routes

📚 Documentation

🛣️ Roadmap

• ✅ TypeScript Client Generation (current)
• ✅ SvelteKit Full-Stack Integration (current)
• 🚧 CLI Tooling - Project templates, deployment orchestration
• 🚧 Python Client Generation - Full Python ecosystem
• 🚧 Advanced Streaming - WebSockets, real-time features

Build modern, type-safe web applications using the Python ecosystem you know + the SvelteKit performance you want.