Common JSON Syntax Errors and How to Fix Them
Learn the JSON mistakes that break parsing most often, including commas, quotes, braces, brackets, and invalid values.
Missing or Extra Commas
JSON requires commas between properties and array items, but it does not allow a trailing comma after the final item.
If a payload fails to parse, check the line before the reported error too. The actual comma mistake is often one item earlier.
Quotes and Brackets
JSON keys must use double quotes, and string values must also use double quotes. Single quotes are valid in JavaScript, but not valid JSON.
Mismatched braces or brackets are another common issue. Formatting the JSON makes nested objects and arrays easier to inspect.
Invalid Values
JSON supports strings, numbers, booleans, null, arrays, and objects. Values such as undefined, comments, and unquoted dates are not valid JSON.
When copying from logs, remove surrounding labels, timestamps, or code snippets before validating the payload.
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FAQs
Can a JSON formatter fix every error automatically?
No. A formatter can show where parsing fails, but you still need to correct invalid JSON syntax or incomplete data.
Why does JavaScript accept something that JSON rejects?
JavaScript object syntax is more flexible. JSON is a stricter data format with specific rules for keys, strings, values, and commas.