marimo is a Python notebook, like Jupyter, but built around a few decisions that fix most of what annoys me about notebooks.

Why it’s cool #

• Reactive: marimo knows which cells use which variables. Change a cell or move a slider, and every cell that depends on it re-runs; delete a cell, and its variables are gone. No hidden state, no “restart and run all” to check that it actually works top to bottom.
• Just a .py file: a notebook is a plain Python script. It diffs nicely in git, can be linted and formatted like any other code (this repo runs ruff and ty on it), imported as a module, or run with python notebook.py.
• Dependencies inside the notebook: packages are declared inline (PEP 723), so marimo edit --sandbox notebook.py builds an isolated environment with uv and you just run it.
• Apps for free: UI elements (sliders, dropdowns, forms, …) are regular Python values, so any notebook can be shown as an interactive app with marimo run.
• Runs in the browser: via WebAssembly and Pyodide, with no server at all. That’s what makes the embed below possible on a static site like this one.

A live example #

Below is the cellular automaton art notebook from the marimo gallery. It’s the same one used in the marimo embedding docs. It runs entirely in your browser, so the first load takes a few seconds while Python itself is downloaded. Then click Make art!:

The notebook lives in this site’s repo as a plain .py file, and is also served as-is. The marimo shortcode reads it at build time and passes its code to marimo.app in the iframe URL. To play with it locally:

uvx marimo edit --sandbox https://marinegor.dev/notebooks/cellular-automaton-art.py