JavaScript/TypeScript linter (ESLint wrapper) with great defaults
Opinionated but configurable ESLint wrapper with lots of goodies included. Enforces strict and readable code. Never discuss code style on a pull request again! No decision-making. No eslint.config.js to manage. It just works!
It uses ESLint underneath, so issues regarding built-in rules should be opened over there.
XO requires your project to be ESM.
Highlights
- Beautiful output.
- Zero-config, but configurable when needed.
- Enforces readable code, because you read more code than you write.
- No need to specify file paths to lint as it lints all JS/TS, HTML, Markdown, JSON (including
package.json), and CSS files except for commonly ignored paths.
- Flat config customization.
- TypeScript supported by default.
- Includes many useful ESLint plugins, like
unicorn, import-x, ava, n and more.
- Caches results between runs for much better performance.
- Super simple to add XO to a project with
$ npm init xo.
- Fix many issues automagically with
$ xo --fix.
- Open all files with errors at the correct line in your editor with
$ xo --open.
- Specify indent and semicolon preferences easily without messing with the rule config.
- Optionally use the Prettier code style or turn off all Prettier rules with the
compat option.
- Optionally use with ESLint directly
- Great editor plugins.
Install
npm install xo --save-dev
You must install XO locally. You can run it directly with $ npx xo.
For framework-specific linting, see Astro, React, Svelte, and Vue.
Usage
$ xo --help
Usage
$ xo [<file|glob> ...]
Options
--fix Automagically fix issues
--fix-dry-run Automagically fix issues without saving the changes to the file system
--reporter Reporter to use
--space Use space indent instead of tabs [Default: 2]
--config Path to a XO configuration file
--semicolon Use semicolons [Default: true]
--prettier Format with prettier or turn off Prettier-conflicted rules when set to 'compat' [Default: false]
--print-config Print the effective ESLint config for the given file
--version Print XO version
--open Open files with issues in your editor
--quiet Show only errors and no warnings
--max-warnings Number of warnings to trigger nonzero exit code [Default: -1]
--stdin Validate/fix code from stdin
--stdin-filename Specify a filename for the --stdin option
--ignore Ignore pattern globs, can be set multiple times
--suppressions-location Path to a custom ESLint suppressions file
--cwd=<dir> Working directory for files [Default: process.cwd()]
Examples
$ xo
$ xo index.js
$ xo *.js !foo.js
$ xo --space
$ xo --print-config=index.js
$ echo 'const x=true' | xo --stdin --fix
Tips
- Add XO to your project with `npm init xo`.
- Put options in xo.config.js instead of using flags so other tools can read it.
Default code style
Any of these can be overridden if necessary.
- Tab indentation (or space)
- Semicolons (or not)
- Single-quotes
- Trailing comma for multiline statements
- No unused variables
- Space after keyword
if (condition) {}
- Always
=== instead of ==
Check out an example and the ESLint rules.
Workflow
The recommended workflow is to add XO locally to your project and run it with the tests.
Simply run $ npm init xo (with any options) to add XO to create an xo.config.js.
Config
You can configure XO options by creating an xo.config.js or an xo.config.ts file in the root directory of your project, or you can add an xo field to your package.json. XO supports all js/ts file extensions (js,jsx,mjs,cjs,ts,tsx,mts,cts), popular framework extensions (vue,svelte,astro), HTML, Markdown, JSON, and CSS automatically. A XO config is an extension of ESLint's Flat Config. Like ESLint, an XO config exports an array of XO config objects. XO config objects extend ESLint Configuration Objects. This means all the available configuration params for ESLint also work for XO. However, XO enhances and adds extra params to the configuration objects to make them easier to work with.
Config types
XO exports the types FlatXoConfig, XoConfigItem, and other types for you to get TypeScript validation on your config files.
examples:
xo.config.js
/** @type {import('xo').FlatXoConfig} */
const xoConfig = [...]
xo.config.ts
import {type FlatXoConfig} from 'xo';
const xoConfig: FlatXoConfig = [...]
export default [...] satisfies import('xo').FlatXoConfig
files
Type: string | (string | string[])[]
Default: **/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,vue,svelte,astro}
A glob string, array of globs, or ESLint's native format (where nested arrays create AND patterns) indicating which files the config object applies to. By default XO will apply the configuration to all JavaScript, TypeScript, and framework files. To configure other file types, such as HTML, Markdown, JSON, or CSS, set files explicitly. This is compatible with ESLint plugin configs, so you can spread them directly into your XO config.
Tip: If you are adding additional @typescript-eslint rules to your config, these rules will apply to JS files as well unless you separate them appropriately with the files option. @typescript-eslint rules set to 'off' or 0, however, will have no effect on JS linting.
ignores
Type: string | string[]
Some paths are ignored by default, including lockfiles and paths in .gitignore. Additional ignores can be added here.
Tip: For global ignores, keep ignores as the only key in the config item. You can optionally set a name property. Adding more properties will cause ignores to be scoped down to your files selection, which may have unexpected effects.
Global negated ignores are supported in both config files and the CLI for reopening XO's built-in ignored paths. This includes directory globs like !dist/**, file globs like !**/*.min.js, and literal file paths like !dist/src/index.js.
When global ignores are involved, XO uses them in this order:
- Built-in default ignores
- Global config
ignores
- CLI
ignores
XO keeps positive ignores for fast file discovery and only rechecks XO's own default-ignored paths. ESLint makes the final ignore decision.
space
Type: boolean | number
Default: false (tab indentation)
Set it to true to get 2-space indentation or specify the number of spaces.
Global only. For file-specific indentation, use the @stylistic/indent and @html-eslint/indent rules.
This option exists for pragmatic reasons, but I would strongly recommend you read “Why tabs are superior”.
semicolon
Type: boolean
Default: true (Semicolons required)
Set it to false to enforce no-semicolon style.
Global only. For file-specific semicolon rules, use the @stylistic/semi rule.
prettier
Type: boolean | 'compat'
Default: false
Format code with Prettier.
Global only. For file-specific Prettier overrides, configure the prettier/prettier rule.
XO applies its own Prettier options:
Any options you set in a Prettier config still apply for anything XO does not configure (like printWidth or plugins), but XO's own style settings take precedence.
Compat
If the Prettier option is set to compat, instead of formatting your code automatically, XO will turn off all rules that conflict with Prettier code style and allow you to pass your formatting to the Prettier tool directly.
Astro
To lint Astro files, install eslint-plugin-astro:
npm install --save-dev eslint-plugin-astro
Then spread its recommended config in your xo.config.js:
import astroPlugin from 'eslint-plugin-astro';
const xoConfig = [
...astroPlugin.configs.recommended,
];
export default xoConfig;
React
To lint React files, install eslint-config-xo-react:
npm install --save-dev eslint-config-xo-react
Then spread it in your xo.config.js:
import xoReact from 'eslint-config-xo-react';
const xoConfig = [
...xoReact(),
];
export default xoConfig;
[!NOTE]
Until eslint-plugin-react supports ESLint 10 natively, you may need to wrap the config with fixupConfigRules from @eslint/compat.
Svelte
To lint Svelte files, install eslint-plugin-svelte:
npm install --save-dev eslint-plugin-svelte
Then spread its recommended config in your xo.config.js:
import sveltePlugin from 'eslint-plugin-svelte';
const xoConfig = [
...sveltePlugin.configs.recommended,
];
export default xoConfig;
Vue
To lint Vue files, install eslint-plugin-vue:
npm install --save-dev eslint-plugin-vue
Then spread its recommended config in your xo.config.js:
import vuePlugin from 'eslint-plugin-vue';
const xoConfig = [
...vuePlugin.configs['flat/recommended'],
];
export default xoConfig;
Shareable configs
If you want to extend a shareable ESLint config or any other npm package, use xo.config.js instead of package.json, since package.json only supports serializable values and cannot import.
xo.config.js
export {default} from 'my-shareable-config';
You can also extend and override:
import myConfig from 'my-shareable-config';
export default [
...myConfig,
{
rules: {
// Your overrides
},
},
];
TypeScript
XO will automatically lint TypeScript files (.ts, .mts, .cts, and .tsx) with the rules defined in eslint-config-xo-typescript#use-with-xo.
XO will handle the @typescript-eslint/parser project option automatically even if you don't have a tsconfig.json in your project.
You can opt out of XO's automatic tsconfig handling by specifying your own languageOptions.parserOptions.project, languageOptions.parserOptions.projectService, or languageOptions.parserOptions.tsconfigRootDir. Files in a config with these properties will be excluded from automatic tsconfig handling.
Usage as an ESLint Configuration
There are two different ways to use XO's rules with ESLint directly, depending on whether you use the xo CLI.
Without the xo CLI
If you don't use the xo CLI and just want XO's rules in ESLint, use eslint-config-xo. It accepts the same core style options as XO, including Prettier integration:
eslint.config.js
import eslintConfigXo from 'eslint-config-xo';
export default [
...eslintConfigXo({space: true, prettier: true}),
];
[!NOTE]
This replaces the old xoToEslintConfig helper. For example, xoToEslintConfig([{space: true, prettier: true}]) becomes eslintConfigXo({space: true, prettier: true}). For per-file overrides, add normal ESLint config objects alongside it.
With the xo CLI (editor integration)
If you use the xo CLI but your editor only has the ESLint extension (not XO's), add an eslint.config.js that re-exports the adapter. It reads your xo.config.js and generates the matching ESLint config automatically, so your editor shows the same errors as running xo — without duplicating your config.
eslint.config.js
export {default} from 'xo/eslint-adapter';
Tips
Monorepo
Put a xo.config.js with your config at the root and do not add a config to any of your bundled packages.
Including files ignored by default
To include files that XO ignores by default, add them as negative globs in the ignores option:
const xoConfig = [{ignores: ['!vendor/**']}];
export default xoConfig;
This also works for narrower carve-outs:
const xoConfig = [{ignores: ['!dist/src/**', '!dist/src/index.js']}];
export default xoConfig;
Warnings are hidden when there are errors
When XO finds errors, warnings are automatically hidden to reduce noise and let you focus on what matters. Warnings are shown normally when there are no errors. Use --quiet to always suppress warnings, or --max-warnings to treat warnings as errors.
Bulk suppression
XO automatically respects an eslint-suppressions.json file if one exists in the working directory. This lets you suppress existing violations while still enforcing rules on new code — useful for incrementally adopting stricter rules in a large codebase.
To generate the suppressions file, create a temporary eslint.config.js using xo/eslint-adapter and run ESLint with --suppress-all:
npx eslint --suppress-all
Commit the resulting eslint-suppressions.json to share suppressions across your team.
To use a custom suppressions file path, pass --suppressions-location:
xo --suppressions-location config/suppressions.json
FAQ
What does XO mean?
It means hugs and kisses.
Why not Standard?
The Standard style is a really cool idea. I too wish we could have one style to rule them all! But the reality is that the JS community is just too diverse and opinionated to create one code style. They also made the mistake of pushing their own style instead of the most popular one. In contrast, XO is more pragmatic and has no aspiration of being the style. My goal with XO is to make it simple to enforce consistent code style with close to no config. XO comes with my code style preference by default, as I mainly made it for myself, but everything is configurable.
Why not ESLint?
XO is based on ESLint. This project started out as just a shareable ESLint config, but it quickly grew out of that. I wanted something even simpler. Just typing xo and be done. No decision-making. No config. I also have some exciting future plans for it. However, you can still get most of the XO benefits while using ESLint directly with the ESLint shareable config.
Editor plugins
Build-system plugins
Configs
Support
Related
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[](https://github.com/xojs/xo)
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[](https://github.com/xojs/xo)
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