How to Fix the Most Common JSON Errors

JSON looks like JavaScript, which is why so many people write invalid JSON by accident. Parsers are strict: one wrong character and the whole document is rejected. These are the mistakes that cause most errors.

1. A trailing comma

JavaScript allows a comma after the last item, JSON doesn't.

{ "name": "Ann", "age": 30, }   (wrong)
{ "name": "Ann", "age": 30 }    (right)

2. Single quotes

Strings and keys must use double quotes.

{ 'name': 'Ann' }   (wrong)
{ "name": "Ann" }   (right)

3. Unquoted keys

{ name: "Ann" }     (wrong)
{ "name": "Ann" }   (right)

4. Comments

JSON has no comments. Remove // and /* */ lines, or store notes in a normal field such as "_comment".

5. Missing commas or brackets

Every item in an object or list is separated by a comma, and every { and [ needs a matching closing character. Long documents hide a missing bracket easily.

6. Special values and unescaped characters

• undefined, NaN and Infinity aren't valid values. Use null or a string.
• A line break inside a string must be written \n, and a quote inside a string must be written \".
• A backslash must be doubled: "C:\\temp".
• Numbers can't have leading zeros (007) or a trailing dot (1.).

Reading the error message

Error messages give a line and column. The reported spot is where the parser gave up, which is sometimes just after the real mistake. If the message points at the start of a key, look at the end of the line before it for a missing comma.

How to fix it

1. Paste the JSON into the JSON Formatter.
2. Read the line and column it reports and fix that one problem.
3. Repeat until it says "Valid JSON", then click Prettify.
4. Compare the fixed version with the original using JSON Diff if you want to be sure nothing else changed.