What Is JSONC? JSON vs JSON5 vs JSONC Explained

JSONC stands for JSON with Comments. It is a specification designed to solve the biggest annoyance developers face when authoring configuration files in standard JSON: the total ban on comments.

1{
2  "name": "John",
3  "age": 30
4}

1{
2  // User information (SyntaxError in Standard JSON!)
3  "name": "John",
4  "age": 30
5}

In a JSONC-aware parser, comments are simply treated as trivia/whitespace and safely ignored during data extraction, leaving the underlying key-value data intact.

JSONC supports both single-line and multi-line comments anywhere whitespace is allowed:

1{
2  // Single-line comment explaining this setting
3  "name": "John"
4}

1{
2  /*
3    Multi-line block comment:
4    Explains the entire user schema
5  */
6  "name": "John"
7}

1{
2  // Application configuration
3  "name": "My App",
4  "version": "1.0.0",
5
6  // Server settings
7  "server": {
8    "port": 3000,
9    "host": "localhost"
10  }
11}

Douglas Crockford purposefully removed comments from the original JSON specification in 2001 to prevent developers from using comments as parsing directives (similar to what happened with HTML comments).

This worked wonderfully for machine-to-machine APIs. But as modern development shifted toward declaring project configs in JSON (like tsconfig.json, VS Code settings.json, and npm configs), developers struggled without the ability to document settings.

1{
2  "server": {
3    "port": 3000,
4    "timeout": 5000
5  },
6  "database": {
7    "host": "localhost",
8    "port": 5432
9  }
10}

1{
2  // HTTP server configuration
3  "server": {
4    "port": 3000,
5    "timeout": 5000
6  },
7
8  // Local database configuration
9  "database": {
10    "host": "localhost",
11    "port": 5432
12  }
13}

One of the most common points of confusion in the developer community is comparing JSONC with JSON5. Both allow comments, but their scope is vastly different:

1{
2  // User configuration
3  "name": "John",
4  "age": 30
5}

1{
2  // User configuration
3  name: 'John',
4  age: 30,
5}

This is the single most common cause of confusion. Because JSONC is not formalised by an IETF RFC standard, different tooling handles trailing commas differently:

1{
2  "name": "John", // Trailing comma: accepted by some JSONC tooling, invalid in strict JSON
3}

JSONC is heavily embraced across modern frontend and developer tooling:

1{
2  // Controls the editor font size in pixels
3  "editor.fontSize": 14,
4
5  // Automatically format files upon saving
6  "editor.formatOnSave": true,
7
8  // Default tab size
9  "editor.tabSize": 2
10}

When building production applications, configuration files with comments must often be sanitized into standard RFC 8259 JSON before being sent over HTTP or passed into strict libraries:

1{
2  // Production server configuration
3  "host": "localhost",
4  "port": 3000
5}

1{
2  "host": "localhost",
3  "port": 3000
4}

In Node.js, you can use packages like jsonc-parser (authored by the VS Code team) or strip-json-comments to strip comments before calling JSON.parse().