More than 300 powerful ESLint rules

Most rules target JavaScript and TypeScript, but some also lint CSS, HTML, JSON, Markdown, TOML, and YAML when used with the matching ESLint language plugin.

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npm install --save-dev eslint eslint-plugin-unicorn

Requires ESLint >=10.4, flat config, and ESM.

You might want to check out XO, which includes this plugin.

Use a preset config or configure each rule in eslint.config.js.

If you don't use a preset, set the same languageOptions as shown below.

import unicorn from 'eslint-plugin-unicorn';
import {defineConfig} from 'eslint/config';
import globals from 'globals';

export default defineConfig([
	{
		files: ['**/*.js'],
		languageOptions: {
			globals: globals.builtin,
		},
		plugins: {
			unicorn,
		},
		rules: {
			'unicorn/prefer-module': 'error',
			'unicorn/…': 'error',
		},
	},
	// …
]);

For TypeScript, scope Unicorn to TypeScript files and configure a TypeScript parser for the same config object:

import typescriptEslintParser from '@typescript-eslint/parser';
import unicorn from 'eslint-plugin-unicorn';
import {defineConfig} from 'eslint/config';
import globals from 'globals';

export default defineConfig([
	{
		files: ['**/*.ts'],
		languageOptions: {
			globals: globals.builtin,
			parser: typescriptEslintParser,
		},
		plugins: {
			unicorn,
		},
		rules: {
			'unicorn/prefer-module': 'error',
			'unicorn/…': 'error',
		},
	},
	// …
]);

💼 Configurations enabled in.
✅ Set in the recommended configuration.
🎨 Set in the recommended-css configuration.
🌐 Set in the recommended-html configuration.
🧩 Set in the recommended-json configuration.
📚 Set in the recommended-markdown configuration.
🛠️ Set in the recommended-toml configuration.
📋 Set in the recommended-yaml configuration.
☑️ Set in the unopinionated configuration.
🔧 Automatically fixable by the --fix CLI option.
💡 Manually fixable by editor suggestions.
💭 Requires type information.

While most rules target JavaScript and TypeScript, some also lint other file types when used with the corresponding ESLint language plugin such as @eslint/css, @eslint/json, @eslint/markdown, @html-eslint/eslint-plugin, eslint-plugin-yml, or eslint-plugin-toml.

When linting JSON, CSS, Markdown, HTML, or other non-JavaScript languages in the same ESLint config, scope Unicorn's JavaScript rule config objects with files. Include TypeScript/JSX extensions there only if your config already provides the matching parser/language setup for those files.

For example, keep Unicorn's JavaScript rules scoped separately, and use the non-JavaScript recommended configs for other languages:

import css from '@eslint/css';
import json from '@eslint/json';
import unicorn from 'eslint-plugin-unicorn';
import {defineConfig} from 'eslint/config';

export default defineConfig([
	{
		files: ['**/*.js'],
		plugins: {unicorn},
		extends: ['unicorn/recommended'],
	},
	{
		files: ['**/*.json'],
		plugins: {json, unicorn},
		language: 'json/json',
		extends: ['unicorn/recommended-json'],
	},
	{
		files: ['**/*.css'],
		plugins: {css, unicorn},
		language: 'css/css',
		extends: ['unicorn/recommended-css'],
	},
]);

These rules work on any file type:

• comment-content
• filename-case
• no-abusive-eslint-disable
• no-leading-empty-lines
• prefer-https

These rules also work on specific non-JavaScript languages:

For more CSS rules, see eslint-cssicorn.

Enabled by the recommended-css preset:

• consistent-compound-words: Enforce consistent spelling of compound words in identifiers.
• empty-brace-spaces: Enforce no spaces between braces.
• escape-case: Require escape sequences to use uppercase or lowercase values.
• expiring-todo-comments: Add expiration conditions to TODO comments.
• filename-case: Enforce a case style for filenames and directory names.
• name-replacements: Enforce replacements for variable, property, and filenames.
• no-abusive-eslint-disable: Enforce specifying rules to disable in eslint-disable comments.
• no-asterisk-prefix-in-documentation-comments: Disallow asterisk prefixes and shared indentation in multiline comments.
• no-conflicting-constraints: Disallow conflicting CSS query and HTML form constraints.
• no-empty-file: Disallow empty files.
• no-leading-empty-lines: Disallow empty lines at the beginning of a file.
• no-shorthand-property-overrides: Disallow shorthand properties that override related longhand properties.
• no-transition-all: Disallow all as a transition property.
• no-zero-fractions: Require consistent decimal numbers without redundant zeros.
• number-literal-case: Enforce proper case for numeric literals.
• prefer-https: Prefer HTTPS over HTTP.
• prefer-literal-ascii: Prefer literal printable ASCII characters over escape sequences.
• relative-url-style: Enforce consistent relative URL style.
• single-line-block-comment-style: Enforce a consistent style for single-line block comments.
• text-encoding-identifier-case: Enforce consistent case for text encoding identifiers.

Opt-in:

• comment-content: Enforce better comment content.
• id-match: Require identifiers to match a specified regular expression.
• indent: Enforce consistent indentation in JSON and CSS.
• no-loss-of-precision: Disallow numeric literals that lose precision when represented as IEEE 754 binary64 values.
• no-manually-wrapped-comments: Disallow manually wrapped comments.
• no-missing-local-resource: Disallow references to missing local resources.
• string-content: Enforce better string content.

Enabled by the recommended-html preset:

• consistent-compound-words: Enforce consistent spelling of compound words in identifiers.
• expiring-todo-comments: Add expiration conditions to TODO comments.
• filename-case: Enforce a case style for filenames and directory names.
• name-replacements: Enforce replacements for variable, property, and filenames.
• no-abusive-eslint-disable: Enforce specifying rules to disable in eslint-disable comments.
• no-conflicting-constraints: Disallow conflicting CSS query and HTML form constraints.
• no-empty-file: Disallow empty files.
• no-ineffective-csp-directives: Disallow ineffective CSP directives in <meta> elements.
• no-invalid-integrity: Disallow invalid subresource integrity metadata.
• no-leading-empty-lines: Disallow empty lines at the beginning of a file.
• prefer-https: Prefer HTTPS over HTTP.
• relative-url-style: Enforce consistent relative URL style.
• text-encoding-identifier-case: Enforce consistent case for text encoding identifiers.

Opt-in:

• comment-content: Enforce better comment content.
• id-match: Require identifiers to match a specified regular expression.
• no-invalid-file-input-accept: Disallow invalid accept values on file inputs.
• no-missing-local-resource: Disallow references to missing local resources.

Enabled by the recommended-json preset:

• consistent-compound-words: Enforce consistent spelling of compound words in identifiers.
• empty-brace-spaces: Enforce no spaces between braces.
• escape-case: Require escape sequences to use uppercase or lowercase values.
• expiring-todo-comments: Add expiration conditions to TODO comments.
• filename-case: Enforce a case style for filenames and directory names.
• name-replacements: Enforce replacements for variable, property, and filenames.
• no-abusive-eslint-disable: Enforce specifying rules to disable in eslint-disable comments.
• no-asterisk-prefix-in-documentation-comments: Disallow asterisk prefixes and shared indentation in multiline comments.
• no-empty-file: Disallow empty files.
• no-leading-empty-lines: Disallow empty lines at the beginning of a file.
• no-zero-fractions: Require consistent decimal numbers without redundant zeros.
• number-literal-case: Enforce proper case for numeric literals.
• prefer-escaped-irregular-whitespace: Prefer escape sequences for irregular whitespace characters.
• prefer-https: Prefer HTTPS over HTTP.
• prefer-literal-ascii: Prefer literal printable ASCII characters over escape sequences.
• prefer-short-escape-sequences: Prefer shorter alternatives to Unicode escape sequences.
• single-line-block-comment-style: Enforce a consistent style for single-line block comments.

Opt-in:

• comma-spacing: Enforce consistent spacing before and after commas in JSON.
• comment-content: Enforce better comment content.
• indent: Enforce consistent indentation in JSON and CSS.
• key-name-casing: Enforce a case style for data keys.
• no-loss-of-precision: Disallow numeric literals that lose precision when represented as IEEE 754 binary64 values.
• no-manually-wrapped-comments: Disallow manually wrapped comments.
• string-content: Enforce better string content.

Enabled by the recommended-markdown preset:

• expiring-todo-comments: Add expiration conditions to TODO comments.
• filename-case: Enforce a case style for filenames and directory names.
• name-replacements: Enforce replacements for variable, property, and filenames.
• no-abusive-eslint-disable: Enforce specifying rules to disable in eslint-disable comments.
• no-empty-file: Disallow empty files.
• no-empty-link-text: Disallow empty link text in Markdown.
• no-leading-empty-lines: Disallow empty lines at the beginning of a file.
• prefer-https: Prefer HTTPS over HTTP.
• relative-url-style: Enforce consistent relative URL style.

Opt-in:

• comment-content: Enforce better comment content.
• no-javascript-url: Disallow javascript: URLs in Markdown.
• no-missing-local-resource: Disallow references to missing local resources.
• require-frontmatter-fields: Require configured YAML frontmatter fields.

Enabled by the recommended-toml preset:

• consistent-compound-words: Enforce consistent spelling of compound words in identifiers.
• empty-brace-spaces: Enforce no spaces between braces.
• escape-case: Require escape sequences to use uppercase or lowercase values.
• expiring-todo-comments: Add expiration conditions to TODO comments.
• filename-case: Enforce a case style for filenames and directory names.
• name-replacements: Enforce replacements for variable, property, and filenames.
• no-abusive-eslint-disable: Enforce specifying rules to disable in eslint-disable comments.
• no-empty-file: Disallow empty files.
• no-leading-empty-lines: Disallow empty lines at the beginning of a file.
• no-zero-fractions: Require consistent decimal numbers without redundant zeros.
• number-literal-case: Enforce proper case for numeric literals.
• numeric-separators-style: Enforce the style of numeric separators by correctly grouping digits.
• prefer-escaped-irregular-whitespace: Prefer escape sequences for irregular whitespace characters.
• prefer-https: Prefer HTTPS over HTTP.
• prefer-short-escape-sequences: Prefer shorter alternatives to Unicode escape sequences.

Opt-in:

• comment-content: Enforce better comment content.
• key-name-casing: Enforce a case style for data keys.
• no-loss-of-precision: Disallow numeric literals that lose precision when represented as IEEE 754 binary64 values.
• no-manually-wrapped-comments: Disallow manually wrapped comments.
• string-content: Enforce better string content.

Enabled by the recommended-yaml preset:

• consistent-compound-words: Enforce consistent spelling of compound words in identifiers.
• empty-brace-spaces: Enforce no spaces between braces.
• escape-case: Require escape sequences to use uppercase or lowercase values.
• expiring-todo-comments: Add expiration conditions to TODO comments.
• filename-case: Enforce a case style for filenames and directory names.
• name-replacements: Enforce replacements for variable, property, and filenames.
• no-abusive-eslint-disable: Enforce specifying rules to disable in eslint-disable comments.
• no-empty-file: Disallow empty files.
• no-leading-empty-lines: Disallow empty lines at the beginning of a file.
• no-zero-fractions: Require consistent decimal numbers without redundant zeros.
• number-literal-case: Enforce proper case for numeric literals.
• prefer-https: Prefer HTTPS over HTTP.

Opt-in:

• comment-content: Enforce better comment content.
• key-name-casing: Enforce a case style for data keys.
• no-manually-wrapped-comments: Disallow manually wrapped comments.
• string-content: Enforce better string content.

See the list.

See the ESLint docs for more information about extending config files.

Note: The JavaScript preset configs also enable the correct language options.

This plugin exports a recommended config that enforces good practices.

import unicorn from 'eslint-plugin-unicorn';
import {defineConfig} from 'eslint/config';

export default defineConfig([
	// …
	{
		files: ['**/*.js'],
		plugins: {
			unicorn,
		},
		extends: [
			'unicorn/recommended',
		],
		rules: {
			'unicorn/prefer-module': 'warn',
		},
	},
]);

These presets enable recommended rules compatible with every dialect listed below. Compatible opt-in rules are disabled, and deprecated rules are excluded. Configure file matching, the language plugin, and language separately. These presets do not configure JavaScript globals or core-rule overrides.

For JSONC or JSON5, use recommended-json with language: 'json/jsonc' or language: 'json/json5'. For GFM Markdown, use recommended-markdown with language: 'markdown/gfm'. These choices are independent of the file extension.

For example:

import json from '@eslint/json';
import unicorn from 'eslint-plugin-unicorn';
import {defineConfig} from 'eslint/config';

export default defineConfig({
	files: ['**/*.json'],
	plugins: {json, unicorn},
	language: 'json/json',
	extends: ['unicorn/recommended-json'],
});

You can also extend a preset directly, for example extends: [unicorn.configs['recommended-json']]. Scope JavaScript presets separately as shown in the configuration examples.

This plugin exports an all config that enables every JavaScript-compatible rule, except deprecated ones.

import unicorn from 'eslint-plugin-unicorn';
import {defineConfig} from 'eslint/config';

export default defineConfig([
	// …
	{
		files: ['**/*.js'],
		plugins: {
			unicorn,
		},
		extends: [
			'unicorn/all',
		],
		rules: {
			'unicorn/prefer-module': 'warn',
		},
	},
]);

• eslint-node-test — ESLint rules for the Node.js built-in test runner.
• eslint-package-json — Powerful ESLint rules for package.json.
• eslint-cssicorn — Powerful ESLint rules for CSS.