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.

JSONC / JSON5 Syntax Reference

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JSONC and JSON5 versus strict JSON

Plain JSON is deliberately minimal: no comments, no trailing commas, double quotes only. Two supersets relax those rules for human-edited config files. JSONC adds just comments and trailing commas. JSON5 goes much further, borrowing many JavaScript object-literal conveniences. This reference compares each feature across all three.

How it works

Both supersets are parsed by dedicated tools, never by JSON.parse. JSONC tolerates comments and trailing commas; JSON5 additionally accepts unquoted keys, single quotes and more:

{
  // JSONC and JSON5: a comment
  key: 'value',        // JSON5 only: unquoted key + single quotes
  hex: 0xFF,           // JSON5 only: hexadecimal
  list: [1, 2, 3,],    // trailing comma in both supersets
}

To consume these formats in a strict-JSON pipeline you either run them through a JSON5/JSONC parser or pre-strip the extensions back to canonical JSON.

Tips and notes

VS Code config files (tsconfig.json, settings.json) are JSONC, not JSON.
A trailing comma is the single most common reason JSON.parse rejects a config file.
Reach for JSON5 when humans edit the file often; keep machine-to-machine APIs on strict JSON.
After editing, validate with the right parser so an unquoted key or stray comment is caught early.