JSON vs 
A complete side-by-side comparison of syntax, features, and use cases.
TL;DR: JSON5 is a superset of JSON. Every valid JSON file is valid JSON5. JSON5 adds human-friendly features while maintaining full backward compatibility.
Syntax Comparison
A comprehensive comparison of what each format supports.
| Feature | JSON | JSON5 |
|---|---|---|
| Comments | Not allowed | // and /* */ |
| Trailing commas | Syntax error | Allowed |
| Unquoted keys | Must quote | Valid identifiers |
| Single quotes | Double only | Single or double |
| Multi-line strings | Not allowed | With \ escape |
| Hexadecimal numbers | Not allowed | 0xFF format |
| Infinity/NaN | Not allowed | Allowed |
| Leading decimals | Must be 0.5 | .5 allowed |
| Trailing decimals | Must be 5.0 | 5. allowed |
| Positive sign | Not allowed | +10 allowed |
Code Examples
Configuration File
A typical app configuration showing the readability difference.
JSON
{ "database": { "host": "localhost", "port": 5432, "ssl": true }, "cache": { "ttl": 3600, "maxSize": 100 } }JSON5
{ // Database connection settings database: { host: 'localhost', port: 5432, ssl: true, // Required for prod }, // Cache configuration (seconds) cache: { ttl: 3600, // 1 hour maxSize: 100, // MB }, }Package Manifest
Managing dependencies with documentation.
JSON
{ "name": "my-project", "version": "1.0.0", "dependencies": { "lodash": "^4.17.21", "express": "^4.18.0" } }JSON5
{ name: 'my-project', version: '1.0.0', dependencies: { // Utility library - used for deep merge lodash: '^4.17.21', // Web framework - handles routing express: '^4.18.0', }, }Test Data Fixtures
Test data with explanatory comments.
JSON
{ "users": [ { "id": 1, "name": "Alice", "role": "admin" }, { "id": 2, "name": "Bob", "role": "user" } ] }JSON5
{ users: [ { id: 1, name: 'Alice', role: 'admin', // Full access }, { id: 2, name: 'Bob', role: 'user', // Read only }, ], }Feature Matrix
Detailed breakdown of capabilities and compatibility.
| Category | Feature | JSON | JSON5 | Notes |
|---|---|---|---|---|
| Comments | Single-line (//) | C-style comments | ||
| Multi-line (/* */) | Block comments | |||
| Strings | Double quotes | Standard strings | ||
| Single quotes | Reduces escaping | |||
| Multi-line | Using \ at line end | |||
| Numbers | Integers/Decimals | Standard numbers | ||
| Hexadecimal | 0xFF format | |||
| Infinity/NaN | IEEE 754 values | |||
| Leading/trailing decimal | .5 or 5. syntax | |||
| Objects | Quoted keys | Required in JSON | ||
| Unquoted keys | Valid identifiers only | |||
| Commas | Trailing commas | Arrays and objects |
When to Use Each Format
Use JSON When...
- API communication - Machine-to-machine data exchange where strict parsing is required
- Database storage - Structured data that won't be manually edited
- Web APIs - REST/GraphQL responses and payloads
- Security-critical data - When deterministic parsing matters
- Third-party integration - When the consumer expects strict JSON
Use JSON5 When...
- Configuration files - Settings that humans read and edit regularly
- Test fixtures - Mock data that benefits from inline documentation
- i18n files - Translations with translator notes and context
- Design tokens - Colors, spacing, typography with explanations
- Any hand-edited data - Files maintained by developers
Migrating from JSON to JSON5
Migration is effortless because JSON5 is a superset of JSON.
Rename file extension (optional)
Change .json to .json5 for clarity. Many tools support both.
Update your parser
Replace JSON.parse() with the JSON5 library: npm install json5
// Before const data = JSON.parse(text); // After import JSON5 from 'json5'; const data = JSON5.parse(text);Gradually adopt features
Your existing JSON is already valid. Add comments, trailing commas, and other features as needed.
Configure your editor
Add JSON5 syntax highlighting for .json5 files. Most editors have extensions available.
Pro tip: Start with configuration files in your project. They benefit most from comments and are low-risk to migrate.
Compatibility Notes
Important considerations when choosing between formats.
Interoperability
JSON5 can parse all JSON, but JSON cannot parse JSON5 features. If your data will be consumed by a strict JSON parser, output in JSON format using JSON.stringify().
Performance
JSON parsing is slightly faster since it's native to JavaScript. JSON5 parsing requires a library. For config files loaded once at startup, this difference is negligible.
Bundle Size
The JSON5 library adds ~5KB minified to your bundle. For server-side applications or build tools, this is rarely a concern.
Security
Both formats are equally safe for data interchange. JSON5 does not execute code - it's purely a data format like JSON.
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