What is JSON5? The Developer-Friendly JSON Format

Introduction

JSON5 is a superset of JSON designed to make configuration files easier for humans to write and maintain. It adds features that developers have wanted in JSON for years: comments, trailing commas, unquoted keys, and more. If you've ever been frustrated by JSON's strict syntax, JSON5 is the answer.

JSON vs JSON5: Side by Side

{
  "name": "My App",
  "version": "1.0.0",
  "database": {
    "host": "localhost",
    "port": 5432
  },
  "features": [
    "auth",
    "logging"
  ]
}

{
  // App configuration
  name: 'My App',
  version: '1.0.0',
  database: {
    host: 'localhost',
    port: 5432,
  },
  features: [
    'auth',
    'logging',
  ],
}

JSON5 Features

1. Comments

The most requested JSON feature. Add // line comments and /* */ block comments:

{
  // This is a line comment
  name: 'My App',
  /* This is a
     block comment */
  version: '1.0.0',
}

2. Trailing Commas

No more syntax errors when you add an item to the end of an array or object:

{
  features: [
    'auth',    // Add new items after
    'logging', // without removing commas
    'cache',   // from previous lines
  ],
}

3. Unquoted Keys

Keys don't need quotes if they're valid JavaScript identifiers:

{
  name: 'Alice',        // No quotes needed
  age: 30,
  'special-key': true,  // Quotes for special chars
}

4. Single-Quoted Strings

Use single quotes instead of double quotes:

{
  greeting: 'Hello, World!',
  path: 'C:\Users\name',  // Less escaping
}

5. Hexadecimal Numbers

{
  maxMemory: 0x1000,  // 4096 in decimal
  flags: 0xFF,        // 255 in decimal
}

6. Multi-line Strings

{
  description: 'This is a \
multi-line string',
}

Where JSON5 is Used

• Babel - .babelrc and babel.config.json support JSON5
• TypeScript - tsconfig.json supports comments (a JSON5 feature)
• ESLint - .eslintrc files can use JSON5 syntax
• Prettier - .prettierrc supports JSON5
• Renovate - renovate.json5 configuration

Using JSON5 in Your Project

// Install the json5 package
// npm install json5

// Reading JSON5
const JSON5 = require('json5');
const config = JSON5.parse(fs.readFileSync('config.json5', 'utf8'));

// Writing JSON5
const output = JSON5.stringify(config, null, 2);
fs.writeFileSync('output.json5', output);

// In ESM
import JSON5 from 'json5';

When Not to Use JSON5

• API responses - Use standard JSON for maximum compatibility
• Data exchange - Not all languages have JSON5 parsers
• High-throughput parsing - JSON5 parsing is slower than JSON
• Browser-native parsing - JSON.parse() doesn't support JSON5

Related Resources