@eslint/json

ESLint JSON Language Plugin

Overview

This package contains a plugin that allows you to natively lint JSON, JSONC, and JSON5 files using ESLint.

Important: This plugin requires ESLint v9.15.0 or higher and you must be using the new configuration system.

Installation

For Node.js and compatible runtimes:

npm install @eslint/json -D
# or
yarn add @eslint/json -D
# or
pnpm install @eslint/json -D
# or
bun add @eslint/json -D

For Deno:

deno add @eslint/json

Usage

This package exports these languages:

• "json/json" is for regular JSON files
• "json/jsonc" is for JSON files that support comments (JSONC) such as those used for Visual Studio Code configuration files
• "json/json5" is for JSON5 files

Depending on which types of JSON files you'd like to lint, you can set up your eslint.config.js file to include just the files you'd like. Here's an example that lints JSON, JSONC, and JSON5 files:

// eslint.config.js
import { defineConfig } from "eslint/config";
import json from "@eslint/json";

export default defineConfig([
	{
		plugins: {
			json,
		},
	},

	// lint JSON files
	{
		files: ["**/*.json"],
		language: "json/json",
		rules: {
			"json/no-duplicate-keys": "error",
		},
	},

	// lint JSONC files
	{
		files: ["**/*.jsonc", ".vscode/*.json"],
		language: "json/jsonc",
		rules: {
			"json/no-duplicate-keys": "error",
		},
	},

	// lint JSON5 files
	{
		files: ["**/*.json5"],
		language: "json/json5",
		rules: {
			"json/no-duplicate-keys": "error",
		},
	},
]);

In CommonJS format:

// eslint.config.js
const { defineConfig } = require("eslint/config");
const json = require("@eslint/json").default;

module.exports = defineConfig([
	{
		plugins: {
			json,
		},
	},

	// lint JSON files
	{
		files: ["**/*.json"],
		language: "json/json",
		rules: {
			"json/no-duplicate-keys": "error",
		},
	},

	// lint JSONC files
	{
		files: ["**/*.jsonc", ".vscode/*.json"],
		language: "json/jsonc",
		rules: {
			"json/no-duplicate-keys": "error",
		},
	},

	// lint JSON5 files
	{
		files: ["**/*.json5"],
		language: "json/json5",
		rules: {
			"json/no-duplicate-keys": "error",
		},
	},
]);

Recommended Configuration

To use the recommended configuration for this plugin, specify your matching files and then use the extends: ["json/recommended"] property, like this:

// eslint.config.js
import { defineConfig } from "eslint/config";
import json from "@eslint/json";

export default defineConfig([
	// lint JSON files
	{
		files: ["**/*.json"],
		ignores: ["package-lock.json"],
		plugins: { json },
		language: "json/json",
		extends: ["json/recommended"],
	},

	// lint JSONC files
	{
		files: ["**/*.jsonc"],
		plugins: { json },
		language: "json/jsonc",
		extends: ["json/recommended"],
	},

	// lint JSON5 files
	{
		files: ["**/*.json5"],
		plugins: { json },
		language: "json/json5",
		extends: ["json/recommended"],
	},
]);

Note: You generally want to ignore package-lock.json because it is auto-generated and you typically will not want to manually make changes to it.

Rules

Rule Name	Description	Recommended
no-duplicate-keys	Disallow duplicate keys in JSON objects	yes
no-empty-keys	Disallow empty keys in JSON objects	yes
no-unnormalized-keys	Disallow JSON keys that are not normalized	yes
no-unsafe-values	Disallow JSON values that are unsafe for interchange	yes
sort-keys	Require JSON object keys to be sorted	no
top-level-interop	Require the JSON top-level value to be an array or object	no

Configuration Comments

In JSONC and JSON5 files, you can also use rule configurations comments and disable directives.

/* eslint json/no-empty-keys: "error" */

{
	"foo": {
		"": 1, // eslint-disable-line json/no-empty-keys -- We want an empty key here
	},
	"bar": {
		// eslint-disable-next-line json/no-empty-keys -- We want an empty key here too
		"": 2,
	},
	/* eslint-disable json/no-empty-keys -- Empty keys are allowed in the following code as well */
	"baz": [
		{
			"": 3,
		},
		{
			"": 4,
		},
	],
	/* eslint-enable json/no-empty-keys -- re-enable now */
}

Both line and block comments can be used for all kinds of configuration comments.

Allowing trailing commas in JSONC

The Microsoft implementation of JSONC optionally allows for trailing commas in objects and arrays (files like tsconfig.json have this option enabled by default in Visual Studio Code). To enable trailing commas in JSONC files, use the allowTrailingCommas language option, as in this example:

// eslint.config.js
import { defineConfig } from "eslint/config";
import json from "@eslint/json";

export default defineConfig([
	// lint JSONC files
	{
		files: ["**/*.jsonc"],
		plugins: { json },
		language: "json/jsonc",
		extends: ["json/recommended"],
	},

	// lint JSONC files and allow trailing commas
	{
		files: ["**/tsconfig.json", ".vscode/*.json"],
		plugins: { json },
		language: "json/jsonc",
		languageOptions: {
			allowTrailingCommas: true,
		},
		extends: ["json/recommended"],
	},
]);

Note: The allowTrailingCommas option is only valid for the json/jsonc language.

Frequently Asked Questions

How does this relate to eslint-plugin-json and eslint-plugin-jsonc?

This plugin implements JSON parsing for ESLint using the language plugins API, which is the official way of supporting non-JavaScript languages in ESLint. This differs from the other plugins:

• eslint-plugin-json uses a processor to parse the JSON, meaning it doesn't create an AST and you can't write custom rules for it.
• eslint-plugin-jsonc uses a parser that still goes through the JavaScript linting functionality and requires several rules to disallow valid JavaScript syntax that is invalid in JSON.

As such, this plugin is more robust and faster than the others. You can write your own custom rules when using the languages in this plugin, too.

What about missing rules that are available in eslint-plugin-json and eslint-plugin-jsonc?

Most of the rules in eslint-plugin-json are actually syntax errors that are caught automatically by the parser used in this plugin.

Similarly, many of the rules in eslint-plugin-jsonc specifically disallow valid JavaScript syntax that is invalid in the context of JSON. These are also automatically caught by the parser in this plugin.

Any other rules that catch potential problems in JSON are welcome to be implemented. You can open an issue to propose a new rule.

Editor and IDE Setup

Visual Studio Code

First, ensure you have the ESLint plugin installed.

Then, edit eslint.validate in your settings.json file to include json, jsonc, and json5:

{
	"eslint.validate": ["json", "jsonc", "json5"]
}

JetBrains WebStorm

For any JetBrains WebStorm, configure the ESLint scope to include json, jsonc, and json5, such as:

**/*.{js,ts,jsx,tsx,cjs,cts,mjs,mts,html,vue,json,jsonc,json5}

License

Apache 2.0

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