Open WebUI is a full-stack, self-hosted AI chat platform that provides a feature-rich interface for interacting with local and cloud-based large language models (Ollama, OpenAI-compatible APIs, Anthropic). The system is built as a monolith with a Python FastAPI backend and a Svelte (SvelteKit) frontend, deployed via Docker. It supports retrieval-augmented generation (RAG) with multiple vector database backends (Chroma, Qdrant, Milvus, pgvector, Elasticsearch, etc.), web search integration (20+ providers), document loading (PDF, DOCX, YouTube, web pages), and a plugin system for custom filters, actions, tools, and pipelines. Additional features include user/group management with granular access control, real-time collaboration via WebSockets, automations with RRULE scheduling, calendar, notes, channels, code execution (Pyodide/Jupyter), image generation (ComfyUI), voice/video calls, and comprehensive analytics. The architecture emphasizes extensibility through abstract base classes (vector DB, reranker, storage provider) and a valve-based configuration system for plugins.