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Contributing to JupyterLab

If you're reading this section, you're probably interested in contributing to JupyterLab. Welcome and thanks for your interest in contributing!

Please take a look at the Contributor documentation, familiarize yourself with using JupyterLab, and introduce yourself on the mailing list and share what area of the project you are interested in working on. Please see also the Jupyter Community Guides.

We have labeled some issues as good first issue or help wanted that we believe are good examples of small, self-contained changes. We encourage those that are new to the code base to implement and/or ask questions about these issues.

Tag Issues with Labels

Users without the commit rights to the jupyterlab repository can also tag the issues with labels. For example: To apply the label foo and bar baz to an issue, comment @meeseeksdev tag foo "bar baz" on the issue.

General Guidelines

For general documentation about contributing to Jupyter projects, see the Project Jupyter Contributor Documentation and Code of Conduct.

All source code is written in TypeScript. See the Style Guide.

All source code is formatted using prettier. When code is modified and committed, all staged files will be automatically formatted using pre-commit git hooks (with help from the lint-staged and husky libraries). The benefit of using a code formatter like prettier is that it removes the topic of code style from the conversation when reviewing pull requests, thereby speeding up the review process.

You may also use the prettier npm script (e.g. npm run prettier or yarn prettier or jlpm prettier) to format the entire code base. We recommend installing a prettier extension for your code editor and configuring it to format your code with a keyboard shortcut or automatically on save.

Setting Up a Development Environment

Installing Node.js and jlpm

Building JupyterLab from its GitHub source code requires Node.js.

If you use conda, you can get it with:

conda install -c conda-forge 'nodejs'

If you use Homebrew on Mac OS X:

brew install node

You can also use the installer from the Node.js website.

Installing JupyterLab

JupyterLab requires Jupyter Notebook version 4.3 or later.

If you use conda, you can install notebook using:

conda install -c conda-forge notebook

You may also want to install nb_conda_kernels to have a kernel option for different conda environments

conda install -c conda-forge nb_conda_kernels

If you use pip, you can install notebook using:

pip install notebook

Fork the JupyterLab repository.

Once you have installed the dependencies mentioned above, use the following steps:

git clone<your-github-username>/jupyterlab.git
cd jupyterlab
pip install -e .
jlpm install
jlpm run build  # Build the dev mode assets (optional)
jlpm run build:core  # Build the core mode assets (optional)
jupyter lab build  # Build the app dir assets (optional)


  • A few of the scripts will run "python". If your target python is called something else (such as "python3") then parts of the build will fail. You may wish to build in a conda environment, or make an alias.

  • The jlpm command is a JupyterLab-provided, locked version of the yarn package manager. If you have yarn installed already, you can use the yarn command when developing, and it will use the local version of yarn in jupyterlab/yarn.js when run in the repository or a built application directory.

  • At times, it may be necessary to clean your local repo with the command npm run clean:slate. This will clean the repository, and re-install and rebuild.

  • If pip gives a VersionConflict error, it usually means that the installed version of jupyterlab_server is out of date. Run pip install --upgrade jupyterlab_server to get the latest version.

  • To install JupyterLab in isolation for a single conda/virtual environment, you can add the --sys-prefix flag to the extension activation above; this will tie the installation to the sys.prefix location of your environment, without writing anything in your user-wide settings area (which are visible to all your envs):

  • You can run jlpm run build:dev:prod to build more accurate sourcemaps that show the original Typescript code when debugging. However, it takes a bit longer to build the sources, so is used only to build for production by default.

If you are using a version of Jupyter Notebook earlier than 5.3, then you must also run the following command to enable the JupyterLab server extension:

jupyter serverextension enable --py --sys-prefix jupyterlab

For installation instructions to write documentation, please see Writing Documentation

Run JupyterLab

Start JupyterLab in development mode:

jupyter lab --dev-mode

Development mode ensures that you are running the JavaScript assets that are built in the dev-installed Python package. When running in dev mode, a red stripe will appear at the top of the page; this is to indicate running an unreleased version.

Build and Run the Tests

jlpm run build:test
jlpm test

You can run tests for an individual package by changing to the appropriate folder in tests:

cd tests/test-notebook
jlpm test

You can also select specific test file(s) to run using a pattern:

cd tests/test-console
jlpm test --pattern=src/*.spec.ts
jlpm test --pattern=src/history.spec.ts

You can run jlpm watch from a test folder, and it will re-run the tests when the source file(s) change. Note that you have to launch the browser of your choice after it says No captured browser. You can put a debugger statement on a line and open the browser debugger to debug specific tests. jlpm watch also accepts the --pattern argument.

Note that there are some helper functions in testutils (which is a public npm package called @jupyterlab/testutils) that are used by many of the tests.

We use karma to run our tests in a browser, mocha as the test framework, and chai for test assertions. We use async/await for asynchronous tests. We have a helper function in @jupyterlab/testutils called testEmission to help with writing tests that use Phosphor signals, as well as a framePromise function to get a Promise for a requestAnimationFrame. We sometimes have to set a sentinel value inside a Promise and then check that the sentinel was set if we need a promise to run without blocking.

To create a new test for a package in packages/, use the following command, where <package-directory-name> is the name of the folder in packages/:

jlpm create:test <package-directory-name>

Build and run the stand-alone examples

To install and build the examples in the examples directory:

jlpm run build:examples

To run a specific example, change to the examples directory (i.e. examples/filebrowser) and enter:



All methods of building JupyterLab produce source maps. The source maps should be available in the source files view of your browser's development tools under the webpack:// header.

When running JupyterLab normally, expand the ~ header to see the source maps for individual packages.

When running in --dev-mode, the core packages are available under packages/, while the third party libraries are available under ~. Note: it is recommended to use jupyter lab --watch --dev-mode while debugging.

When running a test, the packages will be available at the top level (e.g. application/src), and the current set of test files available under /src. Note: it is recommended to use jlpm run watch in the test folder while debugging test options. See above for more info.

High level Architecture

The JupyterLab application is made up of two major parts:

  • an npm package
  • a Jupyter server extension (Python package)

Each part is named jupyterlab. The developer tutorial documentation provides additional architecture information.

The NPM Packages

The repository consists of many npm packages that are managed using the lerna build tool. The npm package source files are in the packages/ subdirectory.

Build the NPM Packages from Source

git clone
cd jupyterlab
pip install -e .
jlpm run build:packages


jlpm run clean
jlpm run build:packages

Writing Documentation

Documentation is written in Markdown and reStructuredText. In particular, the documentation on our Read the Docs page is written in reStructuredText. To ensure that the Read the Docs page builds, you'll need to install the documentation dependencies with conda. These dependencies are located in docs/environment.yml. You can install the dependencies for building the documentation by creating a new conda environment:

conda env create -f docs/environment.yml

The Developer Documentation includes a guide to writing documentation including writing style, naming conventions, keyboard shortcuts, and screenshots.

To test the docs run:

py.test --check-links -k .md . || py.test --check-links -k .md --lf .

The Read the Docs pages can be built using make:

cd docs
make html

Or with jlpm:

jlpm run docs

The Jupyter Server Extension

The Jupyter server extension source files are in the jupyterlab/ subdirectory. To use this extension, make sure the Jupyter Notebook server version 4.3 or later is installed.

Build the JupyterLab server extension

When you make a change to JupyterLab npm package source files, run:

jlpm run build

to build the changes, and then refresh your browser to see the changes.

To have the system build after each source file change, run:

jupyter lab --dev-mode --watch

Build Utilities

There is a range of build utilities for maintaining the repository. To get a suggested version for a library use jlpm run get:dependency foo. To update the version of a library across the repo use jlpm run update:dependency foo ^latest. To remove an unwanted dependency use jlpm run remove:dependency foo.

The key utility is jlpm run integrity, which ensures the integrity of the packages in the repo. It will:

  • Ensure the core package version dependencies match everywhere.
  • Ensure imported packages match dependencies.
  • Ensure a consistent version of all packages.
  • Manage the meta package.

The packages/metapackage package is used to build all of the TypeScript in the repository at once, instead of 50+ individual builds.

The integrity script also allows you to automatically add a dependency for a package by importing from it in the TypeScript file, and then running: jlpm run integrity from the repo root.

We also have scripts for creating and removing packages in packages/, jlpm run create:package and jlpm run remove:package.

Testing Changes to External Packages

Linking/Unlinking Packages to JupyterLab

If you want to make changes to one of JupyterLab's external packages (for example, Phosphor) and test them out against your copy of JupyterLab, you can easily do so using the link command:

  1. Make your changes and then build the external package
  2. Register a link to the modified external package
    • navigate to the external package dir and run jlpm link
  3. Link JupyterLab to modded package
    • navigate to top level of your JupyterLab repo, then run jlpm link "<package-of-interest>"

You can then (re)build JupyterLab (eg jlpm run build) and your changes should be picked up by the build.

To restore JupyterLab to its original state, you use the unlink command:

  1. Unlink JupyterLab and modded package
    • navigate to top level of your JupyterLab repo, then run jlpm unlink "<package-of-interest>"
  2. Reinstall original version of the external package in JupyterLab
    • run jlpm install --check-files

You can then (re)build JupyterLab and everything should be back to default.

Possible Linking Pitfalls

If you're working on an external project with more than one package, you'll probably have to link in your copies of every package in the project, including those you made no changes to. Failing to do so may cause issues relating to duplication of shared state.

Specifically, when working with Phosphor, you'll probably have to link your copy of the "@phosphor/messaging" package (in addition to whatever packages you actually made changes to). This is due to potential duplication of objects contained in the MessageLoop namespace provided by the messaging package.


  • By default, the application will load from the JupyterLab staging directory (default is <sys-prefix>/share/jupyter/lab/build. If you wish to run the core application in <git root>/jupyterlab/build, run jupyter lab --core-mode. This is the core application that will be shipped.

  • If working with extensions, see the extension documentation on

  • The npm modules are fully compatible with Node/Babel/ES6/ES5. Simply omit the type declarations when using a language other than TypeScript.

  • For more information, read the documentation.