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CONTRIBUTING.md

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Contributing Guide

We welcome all kinds of contributions. You don't need to be an expert in frontend or Python development to help out.

Checklist

Contributions are made through pull requests. Before sending a pull request, make sure to do the following:

Please reach out to the marimo team before starting work on a large contribution. Get in touch at GitHub issues or on Discord.

Setup

Note: We recommend that Windows developers use WSL and clone the marimo repository into the WSL environment and not the Windows mount.

Prerequisites

Getting started

make fe && make py
make dev

This will build the frontend, install Python dependencies in editable mode, and launch the dev server (backend on port 2718, frontend on port 3000).

Tip

On the marimo team we use uv + node/pnpm directly. Alternatively, pixi can manage the Python and Node toolchains for you (pixi shell then proceed as above), and Gitpod provides a cloud-based dev environment — but we don't officially support either of these and recommend the setup above.

pre-commit hooks

You can optionally install pre-commit hooks to automatically run the validation checks when making a commit:

uvx pre-commit install

To build the frontend unminified, run:

NODE_ENV=development make fe -B

make commands

Note

Refer to the Makefile for the implementation details

Command Category Description
help General 📖 Show available commands
install-all Setup 🚀 First-time setup: Install all dependencies (frontend & Python)
check-prereqs Setup ✓ Check if all required tools are installed
py Setup 🐍 Install Python dependencies in editable mode
fe Build 🔧 Build frontend assets
test Test 🧪 Run all tests (frontend, Python, end-to-end)
check Test 🧹 Run all checks
fe-check Lint/Test 🧹 Check frontend (lint, typecheck)
fe-test Test 🧪 Test frontend
e2e Test 🧪 Test end-to-end
fe-lint Lint 🧹 Lint frontend
fe-typecheck Lint 🔍 Typecheck frontend
fe-codegen Build 🔄 Generate frontend API
py-check Lint 🔍 Typecheck, lint, format python
typos Lint 🔍 Check for typos
py-test Test 🧪 Test python
py-snapshots Test 📸 Update snapshots
wheel Build 📦 Build wheel
docs Docs 📚 Build docs
docs-serve Docs 📚 Serve docs
storybook Docs 🧩 Start Storybook for UI development

Lint, Typecheck, Format

All checks.

make check

Frontend.

make fe-check

Python.

Using make Using uv 
make py-check         
uv run ruff check --fix
uv run ruff format
uv run --only-group typecheck mypy marimo --exclude=marimo/_tutorials/

Tests

We have frontend unit tests, Python unit tests, and end-to-end tests. Code changes should be accompanied by unit tests. Some changes should also be accompanied by end-to-end tests.

To run all tests:

make test

This can take some time. To run just frontend tests, just Python tests, or just end-to-end tests, read below.

Frontend

In the root directory, run:

make fe-test

Python

We use pytest syntax for Python tests.

Using Make

make py-test

Using uv

Run a specific test

uv run --python 3.13 --group test pytest tests/_ast/

Run all changed tests

uv run --python 3.13 --group test pytest --picked

Run tests with optional dependencies

uv run --python 3.13 --group test-optional pytest tests/_ast/

End-to-end

We use playwright to write and run end-to-end tests, which exercise both the marimo library and the frontend.

(The first time you run, you may be prompted by playwright to install some dependencies; follow those instructions.)

For best practices on writing end-to-end tests, check out the Best Practices doc.

For frontend tests, you want to build the frontend first with make fe so that Playwright works on your latest changes.

Run end-to-end tests.

In the root directory, run:

make e2e

Run tests interactively.

In frontend/:

pnpm playwright test --ui

Run a specific test.

In frontend/:

Without debugger With debugger 
pnpm playwright test $FILENAME        
pnpm playwright test --debug $FILENAME

Storybook

To open Storybook, run the following:

cd frontend && pnpm storybook

Hot reloading / development mode

You can develop on marimo with hot reloading on the frontend and/or development mode on the server (which automatically restarts the server on code changes). These modes are especially helpful when you're making many small changes and want to see changes end-to-end very quickly.

For the frontend, you can choose to run slower hot reloading for an environment closer to production.

Production Development 
pnpm build:watch      
pnpm dev

For the backend, we recommend running without auth (--no-token):

Production Debug 
marimo edit --no-token   
marimo -d edit --no-token

FAQ

  • When to run with hot-reloading?: When you are developing on the frontend and want to see changes immediately. This is useful for styling, layout, new plugins, etc. Developing through the Vite server may have inconsistent behavior due to proxied api/websocket request and since the marimo Python server is not serving the HTML.
  • When to develop with the frontend in watch mode?: When you are making few frontend changes, or when you want to test the frontend in a way that is closer to production.
  • When to run marimo CLI with development mode?: When you are making changes to the backend and want to see debug logs. When developing on marimo plugins, you can run with "On module change" as "autorun" to see changes immediately.

Caveats for running pnpm dev

Running pnpm dev will serve the frontend from a Vite dev server, not from the marimo server. This means that:

  1. You will want to run your marimo server with --headless and --no-token so it does not open a new browser tab, as it will interfere with the frontend dev server.
  2. The tradeoff of using the frontend dev server is that it is faster to develop on the frontend, but you will not be able to test the frontend in the same way that it will be used in production.

Editor settings

If you use vscode, you might find the following settings.json useful:

{
  "editor.formatOnSave": true,
  "editor.formatOnPaste": false,
  "[typescript]": {
    "editor.defaultFormatter": "biomejs.biome"
  },
  "[typescriptreact]": {
    "editor.defaultFormatter": "biomejs.biome"
  }
}

PRs

When submitting a pull request, marimo will run: lint, typecheck, and test jobs.

We have some labels which can influence which tests are run:

  • test-all: Run all tests across unchanged files as well.

Your first PR

Marimo has a variety of CI jobs that run on pull requests. All new PRs will fail until you have signed the CLA. Don't fret. You can sign the CLA by leaving a comment in the PR with text of I have read the CLA Document and I hereby sign the CLA