Marimo is a reactive Python notebook that treats cells like spreadsheet formulas: change one cell or interact with a UI widget and every dependent cell automatically re-executes, eliminating the hidden state bugs that make traditional notebooks unreliable. Backed by over 22,000 GitHub stars, notebooks are stored as pure Python files with PEP 723 inline metadata, making them Git-diffable, importable as modules, executable as CLI scripts with parameterized arguments, and testable with PyTest. Built-in SQL cells query Polars, Pandas, PyArrow, DuckDB, SQLite, PostgreSQL, and MySQL databases, with results automatically flowing into the reactive dependency graph. The AI-native editor provides GitHub Copilot autocomplete, context-aware assistants that access live runtime variables, inline code edits powered by configurable models from OpenAI, Anthropic, or local Ollama instances, and a pair mode that lets external AI agents connect over WebSocket. Notebooks become read-only interactive web applications with marimo run, collaborative authoring environments with marimo edit, or embedded flows inside existing FastAPI applications through ASGI middleware. Gallery mode serves multiple notebooks from a single instance with an auto-generated index page. The Docker image ships with SQL support, token-based authentication, health check endpoints at /health and /api/status, and configurable WebSocket or SSE kernel transport for proxy compatibility. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache 2.0 licensed.