This package contains a plugin that allows you to natively lint JSON and JSONC files using ESLint.
Important: This plugin requires ESLint v9.6.0 or higher and you must be using the new configuration system.
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 install @eslint/json -D
For Deno:
deno add @eslint/json
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:
import json from "@eslint/json";
export default [
{
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:
const json = require("@eslint/json").default;
module.exports = [
{
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",
},
},
];
To use the recommended configuration for this plugin, specify your matching files
and then use the json.configs.recommended
object, like this:
import json from "@eslint/json";
export default [
// lint JSON files
{
files: ["**/*.json"],
ignores: ["package-lock.json"],
language: "json/json",
...json.configs.recommended,
},
// lint JSONC files
{
files: ["**/*.jsonc"],
language: "json/jsonc",
...json.configs.recommended,
},
// lint JSON5 files
{
files: ["**/*.json5"],
language: "json/json5",
...json.configs.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.
-
no-duplicate-keys
- warns when there are two keys in an object with the same text. -
no-empty-keys
- warns when there is a key in an object that is an empty string or contains only whitespace (note:package-lock.json
uses empty keys intentionally)
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.
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:
import json from "@eslint/json";
export default [
// lint JSONC files
{
files: ["**/*.jsonc"],
language: "json/jsonc",
...json.configs.recommended,
},
// lint JSONC files and allow trailing commas
{
files: ["**/tsconfig.json", ".vscode/*.json"],
language: "json/jsonc",
languageOptions: {
allowTrailingCommas: true,
},
...json.configs.recommended,
},
];
Note: The allowTrailingCommas
option is only valid for the json/jsonc
language.
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.
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.
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