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Local Development of Medusa Backend and Monorepo

In this document, you’ll learn how to customize Medusa’s core and run tests.


As an open-source platform, Medusa’s core can be completely customized.

Whether you want to implement something differently, introduce a new feature as part of Medusa’s core or any of the other packages, or contribute to Medusa, this guide helps you learn how to run Medusa’s integration tests, as well as test your own Medusa core in a local backend.

Medusa Repository Overview

Medusa’s repository on GitHub includes all packages related to Medusa under the packages directory. This includes the core Medusa package, the JS Client, the CLI tools, and much more.

All the packages are part of a Yarn workspace. So, when you run a command in the root of the project, such as yarn build, it goes through all registered packages in the workspace under the packages directory and runs the build command in each of those packages.



When using and developing with the Medusa repository, it’s highly recommended that you use Yarn to avoid any errors or issues.

Fork and Clone Medusa’s Repository

To customize Medusa’s core or contribute to it, you must first fork and then clone the GitHub repository.

Install Dependencies and Build Packages

In the directory of the forked GitHub repository, run the following commands to install necessary dependencies then build all packages in the repository:

yarn install
yarn build

Medusa’s Dev CLI tool

Medusa provides a CLI tool to be used for development. This tool facilitates testing your local installment and changes to Medusa’s core without having to publish the changes to NPM.


The Medusa Dev CLI tool only works with yarn v1. You can use the following command to change the yarn version:

yarn set version classic

To install Medusa’s dev CLI tool:

npm install medusa-dev-cli -g

Set the Location of the Medusa Repository

In the directory of your forked GitHub repository, run the following command to specify to the dev CLI tool the location of your Medusa repository:

medusa-dev --set-path-to-repo `pwd`

Run Tests in the Repository

In this section, you’ll learn how to run tests in the Medusa repository. This is helpful after you customize any of Medusa’s packages and want to make sure everything is still working as expected.

Set System Environment Variables

Before you can run the tests, make sure you set the following system environment variables:


Run Unit Tests

To run unit tests in all packages in the Medusa repository, run the following command in the root directory of the repository:

yarn test

This runs the test script defined in the package.json file of each package under the packages directory.

Alternatively, if you want to run the unit tests in a specific package, you can run the test command in the directory of that package.

For example, to run the unit tests of the Medusa core:

cd packages/medusa
yarn test

Run API Integration Tests

API integration tests are used to test out Medusa’s core API Routes.

To run the API integration tests, run the following command in the root directory of the repository:

yarn test:integration:api

Run Plugin Integration Tests

Plugin integration tests are used to test out Medusa’s official plugins, which are also stored in the packages directory in the repository.

To run the plugin integration tests, run the following command in the root directory of the repository:

yarn test:integration:plugins

Test in a Local Backend

Using Medusa’s dev CLI tool, you can test any changes you make to Medusa’s packages in a local backend installation. This eliminates the need to publish these packages on NPM publicly to be able to use them.

Medusa’s dev CLI tool scans and finds the Medusa packages used in your Medusa backend. Then, it copies the files of these packages from the packages directory in the Medusa repository into the node_modules directory of your Medusa backend.


Medusa’s Dev CLI tool uses the path you specified earlier to copy the files of the packages.

Copy Files to Local Backend

To test in a local backend:

  1. Change to the directory of the backend you want to test your changes in:
cd medusa-backend

2. Run the following command to copy the files from the packages directory of your Medusa repository into node_modules:


By default, Medusa’s dev CLI runs in watch mode. So, it copies the files when you first run it. Then, whenever you make changes in the dist directory of the packages in the Medusa repository, it copies the changed files again.

Watch and Compile Changes

While the above command is running, it's recommended to run the watch command inside the directory of every package you're making changes to.

The combination of these two commands running at the same time will compile the package into the dist directory of the package, then copy the compiled changes into your local backend.

For example, if you're making changes in the medusa package, run the following command inside the directory of the medusa package:

yarn watch

Make sure the medusa-dev command is also running to copy the changes automatically.

Alternatively, you can manually run the build command every time you want to compile the changes:

yarn build

CLI Options

Here are some options you can use to customize how Medusa’s dev CLI tool works:

  • --scan-once or -s: Copies files only one time then stops processing. If you make any changes after running the command with this option, you have to run the command again.
medusa-dev -s
  • --quiet or -q: Disables showing any output.
medusa-dev -q
  • --packages: Only copies specified packages. It accepts at least one package name. Package names are separated by a space.
medusa-dev --packages @medusajs/medusa-cli medusa-file-minio

See Also

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