A bank R&D team needed non-technical staff to query internal databases without writing SQL. I built the backend with async FastAPI, SQLAlchemy 2.0, and multi-LLM routing (OpenAI, Ollama, OpenRouter) via LiteLLM, with AST-based SQL validation to guarantee read-only, injection-safe execution. The React/TypeScript frontend uses CodeMirror 6 for an interactive SQL editor alongside a conversational chat interface, with real-time SSE streaming for responses. Stack: FastAPI, React, TypeScript, PostgreSQL, LiteLLM, JWT.