What does "trailing comma" mean in JSON?

A comma after the last item in an array or object with nothing following it. [1, 2, 3,] has a trailing comma after 3. JSON requires every comma to be followed by another value.

Why does JavaScript allow trailing commas but JSON does not?

JavaScript was updated (ES5) to allow trailing commas in arrays and objects. JSON predates that change and has never been updated — it still follows the stricter original syntax.

Which JSON parsers reject trailing commas?

All strict JSON parsers: JSON.parse() in every browser, Python json.loads(), Go encoding/json, Java Jackson, and any parser following RFC 8259. Only lenient parsers like JSON5 or JSONC tolerate them.

Will fixing trailing commas change my data?

No. Removing a trailing comma changes only the syntax, not the values, keys, or structure of your data.

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Frequently Asked Questions

What does "trailing comma" mean in JSON?: A comma after the last item in an array or object with nothing following it. [1, 2, 3,] has a trailing comma after 3. JSON requires every comma to be followed by another value.
Why does JavaScript allow trailing commas but JSON does not?: JavaScript was updated (ES5) to allow trailing commas in arrays and objects. JSON predates that change and has never been updated — it still follows the stricter original syntax.
Which JSON parsers reject trailing commas?: All strict JSON parsers: JSON.parse() in every browser, Python json.loads(), Go encoding/json, Java Jackson, and any parser following RFC 8259. Only lenient parsers like JSON5 or JSONC tolerate them.
Will fixing trailing commas change my data?: No. Removing a trailing comma changes only the syntax, not the values, keys, or structure of your data.