svelte-langgraph

Opinionated SvelteKit/Flowbite based LLM frontend for LangGraph server.

Demo

https://svelte-langgraph-demo.synergyai.nl/

Architecture

• Backend: Python 3.12 + LangGraph server for AI workflow management
• Frontend: SvelteKit + TypeScript with Tailwind CSS and Flowbite components
• Authentication: Descope integration
• Internationalization: Paraglide-JS for multi-language support

Prerequisites

• Install moonrepo, which installs all other dependencies:
  • Python 3.12
  • Node.js 24 LTS
  • uv (Python package manager)
  • pnpm (Node.js package manager)

Configuration

Both the frontend and backend require environment variables to be configured. Copy the example files and update them with your values:

Backend Environment Variables

Copy the example file:

cd apps/backend
cp .env.example .env

Configure the following variables in apps/backend/.env:

• DESCOPE_PROJECT_ID - Your Descope project ID for authentication
• OPENAI_API_KEY - Your OpenAI-compatible API key (e.g., OpenAI, OpenRouter)
• OPENAI_BASE_URL - OpenAI-compatible API base URL (optional, defaults to OpenAI)
• CHAT_MODEL_NAME - OpenAI-compatible model to use (defaults to gpt-4o-mini)
• LANGSMITH_API_KEY - Your LangSmith API key for tracing (optional)
• LANGSMITH_ENDPOINT - LangSmith endpoint URL (defaults to EU region)

AI Provider Configuration

This application supports multiple OpenAI-compatible providers. Configure your preferred provider using the environment variables above.

Using OpenAI (Default)

To use OpenAI directly (no additional configuration needed):

# .env
OPENAI_API_KEY=your_openai_api_key
# OPENAI_BASE_URL not needed for OpenAI (uses default)
CHAT_MODEL_NAME=gpt-4o-mini  # Default OpenAI model

Popular OpenAI models:

• gpt-4o-mini - Fast, cost-effective model (default)
• gpt-4o - Most capable model
• gpt-3.5-turbo - Legacy model

Using OpenRouter

OpenRouter provides access to multiple AI models including free options:

# .env
OPENAI_API_KEY=your_openrouter_api_key
OPENAI_BASE_URL=https://openrouter.ai/api/v1
CHAT_MODEL_NAME=x-ai/grok-4-fast:free  # Free Grok model

Popular OpenRouter models:

• x-ai/grok-4-fast:free - Free Grok model
• meta-llama/llama-3.2-3b-instruct:free - Free Llama model
• anthropic/claude-3.5-sonnet - Claude 3.5 Sonnet (paid)

Using Ollama

For local AI models using Ollama:

# .env
OPENAI_API_KEY=ollama  # Can be any value for local usage
OPENAI_BASE_URL=http://localhost:11434/v1
CHAT_MODEL_NAME=llama3.2  # Your local Ollama model

Frontend Environment Variables

Copy the example file:

cd apps/frontend
cp .env.example .env

Configure the following variables in apps/frontend/.env:

• AUTH_TRUST_HOST=true - Enable auth trust host for development
• AUTH_DESCOPE_ID - Your Descope project ID
• AUTH_DESCOPE_SECRET - Your Descope management key
• AUTH_DESCOPE_ISSUER - Optional: The Descope Issuer URL for your project.
  Normally you don’t need to set this, since the SDK defaults to the global US endpoint.
  If your Descope tenant is in the EU region (or another region with a specific issuer),
  you must set this to the region-specific issuer URL provided in your Descope console.
  Can be found in your Descope account under the Applications page.
  Example for EU:
  AUTH_DESCOPE_ISSUER=https://api.euc1.descope.com/<your-project-id> Only set this if your tenant requires it, otherwise leave it unset.
• AUTH_SECRET - Random string for session encryption (generate with npx auth secret)
• PUBLIC_LANGCHAIN_API_KEY - Your LangChain API key for client-side requests
• PUBLIC_LANGGRAPH_API_URL - URL of your LangGraph server (typically http://localhost:8123)
• PUBLIC_SENTRY_DSN - Public DSN for your Sentry project, for error tracking and user feedback.
• PUBLIC_SENTRY_SEND_PII - Optional: Enable PII (Personally Identifiable Information) capture in Sentry.
• SENTRY_AUTH_TOKEN - Sentry auth token for source map uploads.
• SENTRY_ORG - Sentry org for source map uploads.
• SENTRY_PROJECT - Sentry project for source map uploads.

Getting Started

Start dev servers

The following command ensures dependencies are installed and starts dev servers for frontend and backend, with hot reload:

moon :dev

Run local checks

Run all checks (linting, type checking, formatting):

moon check --all

Tooling

Backend Development

The backend uses LangGraph for AI workflow orchestration with the following key dependencies:

• LangChain with OpenAI-compatible integration (OpenRouter, OpenAI, etc.)
• Descope for authentication
• Python-dotenv for environment management

Frontend Development

The frontend is built with modern web technologies:

• SvelteKit for the application framework
• Tailwind CSS for styling
• Flowbite for UI components
• Playwright for end-to-end testing
• Vitest for unit testing

Production

To run a Docker build of the project, use Docker Compose:

docker compose build

To run it:

docker compose up [--build]

For now, we will not be running the backend in Docker, so to test with the dev backend, it's required to make it available to the Docker container and inform the Docker container of your IP:

moon backend:dev -- --host 0.0.0.0

And in a different terminal:

PUBLIC_LANGGRAPH_API_URL=http://host.docker.internal:2024 docker compose up --build

Internationalization with Paraglide

This project uses Paraglide-JS for type-safe internationalization. Paraglide offers a developer-friendly approach where you can:

• Add or modify translations without touching code - just edit JSON files
• Add new languages by creating a new JSON file and updating one config line
• Change locale names (e.g., "English" → "Inglés") without any code changes

Message Files

All translations are stored in apps/frontend/messages/:

Each file contains key-value pairs for all UI text:

{
  "$schema": "https://inlang.com/schema/inlang-message-format",
  "hello_world": "Hello, {name}!",
  "local_name": "English"
}

The local_name key is special - it defines how each language refers to itself in the language switcher.

Adding a New Language

1. Create a new JSON file in apps/frontend/messages/ (e.g., fr.json for French)
2. Copy the structure from en.json and translate all values
3. Add the locale code to apps/frontend/project.inlang/settings.json:

{
  "locales": ["en", "nl", "hi", "fr"]
}

That's it! The language will automatically appear in the language switcher with the name specified in local_name.