Set up a Development Environment

ESLint has a very lightweight development environment that makes updating code fast and easy. This is a step-by-step guide to setting up a local development environment that will let you contribute back to the project.

Step 1: Install Node.js

Go to to download and install the latest stable version for your operating system.

Most of the installers already come with npm but if for some reason npm doesn’t work on your system, you can install it manually using the instructions on the site.

Step 2: Fork and Checkout Your Own ESLint Repository

Go to and click the “Fork” button. Follow the GitHub documentation for forking and cloning.

Clone your fork:

git clone<Your GitHub Username>/eslint

Once you’ve cloned the repository, run npm install to get all the necessary dependencies:

cd eslint
npm install

You must be connected to the Internet for this step to work. You’ll see a lot of utilities being downloaded.

Note: It’s a good idea to re-run npm install whenever you pull from the main repository to ensure you have the latest development dependencies.

Step 3: Add the Upstream Source

The upstream source is the main ESLint repository where active development happens. While you won’t have push access to upstream, you will have pull access, allowing you to pull in the latest code whenever you want.

To add the upstream source for ESLint, run the following in your repository:

git remote add upstream

Now, the remote upstream points to the upstream source.

Step 4: Install the Yeoman Generator

Yeoman is a scaffold generator that ESLint uses to help streamline development of new rules. If you don’t already have Yeoman installed, you can install it via npm:

npm install -g yo

Then, you can install the ESLint Yeoman generator:

npm install -g generator-eslint

Please see the generator documentation for instructions on how to use it.

Step 5: Run the Tests

Running the tests is the best way to ensure you have correctly set up your development environment. Make sure you’re in the eslint directory and run:

npm test

The testing takes a few minutes to complete. If any tests fail, that likely means one or more parts of the environment setup didn’t complete correctly. The upstream tests always pass.

Reference Information

Directory Structure

The ESLint directory and file structure is as follows:

  • bin - executable files that are available when ESLint is installed
  • conf - default configuration information
  • docs - documentation for the project
  • lib - contains the source code
    • formatters - all source files defining formatters
    • rules - all source files defining rules
  • tests - the main unit test folder
    • lib - tests for the source code
      • formatters - tests for the formatters
      • rules - tests for the rules


Once you have your development environment installed, you can make and submit changes to the ESLint source files. Doing this successfully requires careful adherence to our pull-request submission workflow.

Build Scripts

ESLint has several build scripts that help with various parts of development.

npm test

The primary script to use is npm test, which does several things:

  1. Lints all JavaScript (including tests) and JSON
  2. Runs all tests on Node.js
  3. Checks code coverage targets
  4. Generates build/eslint.js for use in a browser
  5. Runs a subset of tests in PhantomJS

Be sure to run this after making changes and before sending a pull request with your changes.

Note: The full code coverage report is output into /coverage.

npm run lint

Runs just the JavaScript and JSON linting on the repository.

npm run webpack

Generates build/eslint.js, a version of ESLint for use in the browser.

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