| # Architecture |
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| This document provides a high-level overview of the Chat UI codebase. If you're looking to contribute or understand how the codebase works, this is the place for you! |
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| ## Overview |
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| Chat UI provides a simple interface connecting LLMs to external tools via MCP. The project uses [MongoDB](https://www.mongodb.com/) and [SvelteKit](https://kit.svelte.dev/) with [Tailwind](https://tailwindcss.com/). |
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| Key architectural decisions: |
| - **OpenAI-compatible only**: All model interactions use the OpenAI API format |
| - **MCP for tools**: Tool calling is handled via Model Context Protocol servers |
| - **Auto-discovery**: Models are discovered from the `/models` endpoint |
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| ## Code Map |
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| ### `routes` |
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| All routes rendered with SSR via SvelteKit. The majority of backend and frontend logic lives here, with shared modules in `lib` (client) and `lib/server` (server). |
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| ### `textGeneration` |
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| Provides a standard interface for chat features including model output, tool calls, and streaming. Outputs `MessageUpdate`s for fine-grained status updates (new tokens, tool results, etc.). |
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| ### `endpoints` |
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| Provides the streaming interface for OpenAI-compatible endpoints. Models are fetched and cached from `${OPENAI_BASE_URL}/models`. |
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| ### `mcp` |
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| Implements MCP client functionality for tool discovery and execution. See [MCP Tools](../configuration/mcp-tools) for configuration. |
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| ### `llmRouter` |
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| Intelligent routing logic that selects the best model for each request. Uses the Arch router model for classification. See [LLM Router](../configuration/llm-router) for details. |
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| ### `migrations` |
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| MongoDB migrations for maintaining backwards compatibility across schema changes. Any schema changes must include a migration. |
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| ## Development |
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| ```bash |
| npm install |
| npm run dev |
| ``` |
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| The dev server runs at `http://localhost:5173` with hot reloading. |
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