What is the difference between JSONC and JSON5?

JSONC (JSON with Comments) is a small superset that adds only line and block comments plus trailing commas; it is what VS Code uses for tsconfig.json and settings. JSON5 is a much broader superset that also allows unquoted keys, single-quoted strings, hexadecimal numbers, leading or trailing decimal points, and special values like Infinity and NaN.

Can I parse JSONC or JSON5 with JSON.parse?

No. The standard JSON.parse function rejects comments, trailing commas and every other extension. You must either strip the extensions first or use a dedicated parser such as the json5 package or jsonc-parser.

Are comments allowed in JSON?

Not in standard JSON, which has no comment syntax at all. JSONC and JSON5 both add C-style line comments with two slashes and block comments delimited by slash-star and star-slash.

Does JSON5 allow trailing commas?

Yes. Both JSONC and JSON5 allow a comma after the final element of an array or the final member of an object, which makes diffs cleaner and reordering easier.

Are unquoted object keys valid anywhere?

Only in JSON5. Standard JSON and JSONC both require keys to be double-quoted strings. JSON5 permits identifier-style keys without quotes, similar to JavaScript object literals.

What is the JSONC / JSON5 Syntax Reference?

Reference comparing JSONC and JSON5 syntax extensions against strict JSON, including comments, trailing commas, unquoted keys, single quotes, hex numbers and special float values. It runs free in your browser on Gera Tools, with nothing uploaded.

JSONC / JSON5 Syntax Reference

Name: JSONC / JSON5 Syntax Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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JSONC and JSON5 versus strict JSON

Plain JSON is deliberately minimal: no comments, no trailing commas, double-quotes only. That strictness is intentional for machine-to-machine data exchange, but it makes hand-edited configuration files unnecessarily painful. Two supersets relax those rules for humans.

JSONC (JSON with Comments) adds only two things: C-style line comments (//) and block comments (/* ... */), plus trailing commas in objects and arrays. It is the format VS Code uses for settings.json, tsconfig.json, and launch.json.

JSON5 goes much further, drawing on JavaScript object-literal syntax. In addition to everything JSONC allows, JSON5 also permits unquoted keys, single-quoted strings, multi-line strings, hexadecimal numbers, numeric values like Infinity and NaN, and more. It targets configuration files that humans will read and edit extensively.

Feature comparison

Both supersets are parsed by dedicated libraries, never by JSON.parse. A quick cheat sheet:

Feature	JSON	JSONC	JSON5
Line comments (`//`)	No	Yes	Yes
Block comments (`/* */`)	No	Yes	Yes
Trailing comma in objects	No	Yes	Yes
Trailing comma in arrays	No	Yes	Yes
Unquoted keys	No	No	Yes
Single-quoted strings	No	No	Yes
Hexadecimal numbers	No	No	Yes
`Infinity`, `NaN`	No	No	Yes
Leading decimal point (`.5`)	No	No	Yes

Code example

{
  // JSONC and JSON5: comments explain the value
  timeout: 30,          // JSON5 only: unquoted key
  host: 'localhost',    // JSON5 only: single quotes
  hex: 0xFF,            // JSON5 only: hexadecimal integer
  ports: [3000, 3001,], // trailing comma — valid in both supersets
  /* The block below can be toggled off */
  debug: false,
}

Strip this through a JSONC parser and only the comments and trailing commas are accepted; an unquoted key would fail. Run it through a JSON5 parser and every line is valid.

Choosing the right dialect

Stay on strict JSON for any API response, wire protocol, or data file that a machine produces and another machine reads. The standard is unambiguous and every language has a battle-tested parser.

Use JSONC when the file is checked into source control and developers benefit from explanatory comments — toolchain configs, VS Code workspace settings, database seed files, or feature flag definitions. The change-set is minimal and the format is accepted by most modern tooling.

Use JSON5 when you want the full authoring convenience of JavaScript object literals, human readers outnumber machines, and you are comfortable adding the json5 npm package (or equivalent) to your build.

Parsing in code

// Strict JSON — built-in
JSON.parse('{"key":"value"}');

// JSONC — npm i jsonc-parser
import { parse } from "jsonc-parser";
parse('{ "key": "value", // comment\n}');

// JSON5 — npm i json5
import JSON5 from "json5";
JSON5.parse("{ key: 'value', hex: 0xFF, }");

The single most common mistake: editing a .json file to add a comment or a trailing comma and then wondering why JSON.parse throws a SyntaxError. Switch to the JSONC parser if your tooling accepts it, or pre-process with jsonc-parser to strip extensions back to canonical JSON.