marimo

marimo is an open-source reactive Python notebook (Apache 2.0, roughly 20,000–22,000 GitHub stars) that stores notebooks as plain .py files instead of JSON, executes cells in a dependency graph so downstream cells update automatically, and eliminates hidden state for reproducible, pytest-testable notebooks. It bundles first-class SQL cells (DuckDB, PostgreSQL, MySQL, SQLite, Snowflake), interactive widgets without callbacks, marimo run to deploy notebooks as web apps, WASM export, and an AI-native editor with built-in assistants plus marimo pair, which connects agents like Claude Code to live sessions.

In October 2025 marimo was acquired by AI cloud company CoreWeave, and it is used by research teams at Stanford, Berkeley, and SLAC as well as AI engineering teams. Notebooks run interactively, as CLI scripts, as apps, or in the browser via Pyodide.

Limitation: in 2026 a critical pre-authentication RCE (CVE-2026-39987, severity 9.3) in the terminal WebSocket endpoint was exploited in the wild within 10 hours of disclosure — never expose a marimo server to the internet, and upgrade past 0.23.0. It also trades Jupyter's huge extension catalog for cleaner diffs, so teams deep in the Jupyter ecosystem should pilot first.

Install with pip install marimo, then marimo edit to open the editor; or run notebooks in the browser via molab.