# Getting Started with ESLint

ESLint is a tool for identifying and reporting on patterns found in ECMAScript/JavaScript code, with the goal of making code more consistent and avoiding bugs. In many ways, it is similar to JSLint and JSHint with a few exceptions:

* ESLint uses [Espree](https://github.com/eslint/espree) for JavaScript parsing.
* ESLint uses an AST to evaluate patterns in code.
* ESLint is completely pluggable, every single rule is a plugin and you can add more at runtime.

## Installation and Usage

Prerequisites: [Node.js](https://nodejs.org/en/) (`^10.12.0`, or `>=12.0.0`) built with SSL support. (If you are using an official Node.js distribution, SSL is always built in.)

You can install ESLint using npm or yarn:

```
npm install eslint --save-dev

# or

yarn add eslint --dev
```

You should then set up a configuration file, and the easiest way to do that is to use the `--init` flag:

```
$ npx eslint --init

# or

$ yarn run eslint --init
```

**Note:** `--init` assumes you have a `package.json` file already. If you don't, make sure to run `npm init` or `yarn init` beforehand.

After that, you can run ESLint on any file or directory like this:

```
$ npx eslint yourfile.js

# or

$ yarn run eslint yourfile.js
```

It is also possible to install ESLint globally rather than locally (using `npm install eslint --global`). However, this is not recommended, and any plugins or shareable configs that you use must be installed locally in either case.

## Configuration

**Note:** If you are coming from a version before 1.0.0 please see the [migration guide](migrating-to-1.0.0.md).

After running `eslint --init`, you'll have a `.eslintrc.{js,yml,json}` file in your directory. In it, you'll see some rules configured like this:

```json
{
    "rules": {
        "semi": ["error", "always"],
        "quotes": ["error", "double"]
    }
}
```

The names `"semi"` and `"quotes"` are the names of [rules](/docs/rules) in ESLint. The first value is the error level of the rule and can be one of these values:

* `"off"` or `0` - turn the rule off
* `"warn"` or `1` - turn the rule on as a warning (doesn't affect exit code)
* `"error"` or `2` - turn the rule on as an error (exit code will be 1)

The three error levels allow you fine-grained control over how ESLint applies rules (for more configuration options and details, see the [configuration docs](configuring/)).

Your `.eslintrc.{js,yml,json}` configuration file will also include the line:

```json
{
    "extends": "eslint:recommended"
}
```

Because of this line, all of the rules marked "(recommended)" on the [rules page](/docs/rules) will be turned on.  Alternatively, you can use configurations that others have created by searching for "eslint-config" on [npmjs.com](https://www.npmjs.com/search?q=eslint-config).  ESLint will not lint your code unless you extend from a shared configuration or explicitly turn rules on in your configuration.

---

## Next Steps

* Learn about [advanced configuration](configuring/) of ESLint.
* Get familiar with the [command line options](command-line-interface.md).
* Explore [ESLint integrations](integrations.md) into other tools like editors, build systems, and more.
* Can't find just the right rule?  Make your own [custom rule](/docs/developer-guide/working-with-rules.md).
* Make ESLint even better by [contributing](/docs/developer-guide/contributing/).