How to Fix Common JSON Syntax Errors

JSON is strict, and a single stray character breaks the whole file. The good news: almost every error falls into a handful of categories. Here's how to recognize and fix each.

1. Trailing commas

JSON does not allow a comma after the last item:

{ "a": 1, "b": 2, }   ← invalid (comma after 2)
{ "a": 1, "b": 2 }    ← valid

This is the most common error, especially after deleting a line. Remove the final comma in any object or array.

2. Single quotes instead of double

JSON keys and string values must use double quotes. {'a': 1} is invalid; it must be {"a": 1}. Single quotes are valid in JavaScript but not in JSON.

3. Unquoted keys

Every key needs quotes: {name: "Sam"} is invalid; use {"name": "Sam"}. (This trips up people coming from JavaScript object literals.)

4. Missing or mismatched brackets

Every { needs a } and every [ a ]. A missing closing bracket usually shows as an error at the very end of the file. Pretty-printing helps you see the nesting and spot the gap.

5. Wrong value types

• Strings must be quoted: "status": active → "status": "active".
• Use true/false/null lowercase and unquoted for those literals.
• No comments allowed — // like this breaks JSON.
• No trailing decimal or leading zeros: .5 → 0.5.

6. Unescaped characters in strings

Inside a string, a literal double quote or backslash must be escaped: "He said \"hi\"". Newlines inside strings must be \n, not actual line breaks.

Find the error fast

Paste your JSON into our JSON formatter — it validates instantly and points to the line and column of the problem, so you don't have to hunt. Everything runs in your browser, so even sensitive data stays private.

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